Systems and methods of adaptively determining template size for illumination compensation

ABSTRACT

Techniques and systems are provided for processing video data. For example, a current block of a picture of the video data can be obtained for processing by an encoding device or a decoding device. A parameter of the current block can be determined. Based on the determined parameter of the current block, at least one or more of a number of rows of samples or a number columns of samples in a template of the current block and at least one or more of a number of rows of samples or a number columns of samples in a template of a reference picture can be determined. Motion compensation for the current block can be performed. For example, one or more local illumination compensation parameters can be derived for the current block using the template of the current block and the template of the reference picture.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/404,715, filed Oct. 5, 2016, which is hereby incorporated byreference, in its entirety and for all purposes.

FIELD

This application is related to video coding and compression. Morespecifically, this application relates to systems and methods ofperforming improved illumination compensation.

BACKGROUND

Many devices and systems allow video data to be processed and output forconsumption. Digital video data includes large amounts of data to meetthe demands of consumers and video providers. For example, consumers ofvideo data desire video of the utmost quality, with high fidelity,resolutions, frame rates, and the like. As a result, the large amount ofvideo data that is required to meet these demands places a burden oncommunication networks and devices that process and store the videodata.

Various video coding techniques may be used to compress video data.Video coding is performed according to one or more video codingstandards. For example, video coding standards include high-efficiencyvideo coding (HEVC), advanced video coding (AVC), moving picture expertsgroup (MPEG) coding, or the like. Video coding generally utilizesprediction methods (e.g., inter-prediction, intra-prediction, or thelike) that take advantage of redundancy present in video images orsequences. An important goal of video coding techniques is to compressvideo data into a form that uses a lower bit rate, while avoiding orminimizing degradations to video quality. With ever-evolving videoservices becoming available, encoding techniques with better codingefficiency are needed.

BRIEF SUMMARY

Illumination compensation can be used to efficiently compensatevariations in illumination between one or more pictures. In someimplementations, techniques and systems are described herein foradaptively determining the size of one or more templates to use forlocal illumination compensation (LIC). For example, the number of rowsand/or column of pixels in a template used to derive one or more LICparameters for a current block can vary depending on a parameter of thecurrent block. The parameter can include the block size (e.g., thewidth, the height, or the width and height of the block, or othersuitable measure of size), a chroma format of the block (e.g., 4:2:0format, 4:2:2 format, 4:4:4 format, or other suitable chroma format), orother parameter that can be used to determine the template size.

According to at least one example, a method of processing video data isprovided. The method comprises obtaining a current block of a picture ofthe video data. The method further comprises determining a parameter ofthe current block. The method further comprises determining at least oneor more of a number of rows of samples or a number columns of samples ina template of the current block and at least one or more of a number ofrows of samples or a number columns of samples in a template of areference picture based on the determined parameter of the currentblock. The method further comprises performing motion compensation forthe current block. Performing the motion compensation includes derivingone or more local illumination compensation parameters for the currentblock using the template of the current block and the template of thereference picture.

In another example, an apparatus for processing video data is providedthat includes a memory configured to store video data and a processor.The processor is configured to and can obtain a current block of apicture of the video data. The processor is further configured to andcan determine a parameter of the current block. The processor is furtherconfigured to and can determine at least one or more of a number of rowsof samples or a number columns of samples in a template of the currentblock and at least one or more of a number of rows of samples or anumber columns of samples in a template of a reference picture based onthe determined parameter of the current block. The processor is furtherconfigured to and can perform motion compensation for the current block.Performing the motion compensation includes deriving one or more localillumination compensation parameters for the current block using thetemplate of the current block and the template of the reference picture.

In another example, a non-transitory computer-readable medium isprovided having stored thereon instructions that, when executed by oneor more processors, cause the one or more processor to: obtain a currentblock of a picture of the video data; determine a parameter of thecurrent block; determine at least one or more of a number of rows ofsamples or a number columns of samples in a template of the currentblock and at least one or more of a number of rows of samples or anumber columns of samples in a template of a reference picture based onthe determined parameter of the current block; and perform motioncompensation for the current block, wherein performing the motioncompensation includes deriving one or more local illuminationcompensation parameters for the current block using the template of thecurrent block and the template of the reference picture.

In another example, an apparatus for processing video data is provided.The apparatus includes means for obtaining a current block of a pictureof the video data. The apparatus further includes means for determininga parameter of the current block. The apparatus further includes meansfor determining at least one or more of a number of rows of samples or anumber columns of samples in a template of the current block and atleast one or more of a number of rows of samples or a number columns ofsamples in a template of a reference picture based on the determinedparameter of the current block. The apparatus further includes means forperforming motion compensation for the current block. Performing themotion compensation includes deriving one or more local illuminationcompensation parameters for the current block using the template of thecurrent block and the template of the reference picture.

In some aspects, the parameter of the current block includes a size ofthe current block. In some cases, the size of the current block includesa width of the current block. In some examples, the number of rows ofsamples in the template of the current block is one row when the widthof the current block is less than a threshold width. In some examples,the number of rows of samples in the template of the current block ismore than one row when the width of the current block is greater than athreshold width.

In some cases, the size of the current block includes a height of thecurrent block. In some examples, the number of columns of samples in thetemplate of the current block is one column when the height of thecurrent block is less than a threshold height. In some examples, thenumber of columns of samples in the template of the current block ismore than one columns when the height of the current block is greaterthan a threshold height.

In some cases, the size of the current block includes a width of theblock and a height of the block.

In some examples, the parameter of the current block includes a chromaformat of the current block. In one illustrative example, the number ofrows of samples and the number of columns of samples in the template ofthe current block is set to half of a luma size of the current blockwhen the chroma format of the current block is 4:2:0. In anotherexample, the number of rows of samples in the template of the currentblock is set to a same size as a luma size of the current block and thenumber of columns of samples in the template of the current block is setto half of the luma size when the chroma format of the current block is4:2:2.

In some aspects, the method, apparatuses, and computer-readable mediumdescribed above may further comprise decoding the current block usingthe one or more illumination compensation parameters.

In some aspects, the method, apparatuses, and computer-readable mediumdescribed above may further comprise signaling the one or moreillumination compensation parameters in an encoded video bitstream.

This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used in isolationto determine the scope of the claimed subject matter. The subject mattershould be understood by reference to appropriate portions of the entirespecification of this patent, any or all drawings, and each claim.

The foregoing, together with other features and embodiments, will becomemore apparent upon referring to the following specification, claims, andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention are described indetail below with reference to the following drawing figures:

FIG. 1 is a block diagram illustrating an example of an encoding deviceand a decoding device, in accordance with some examples;

FIG. 2A is a conceptual diagram illustrating example spatial neighboringmotion vector candidates for a merge mode, in accordance with someexamples;

FIG. 2B is a conceptual diagram illustrating example spatial neighboringmotion vector candidates for an advanced motion vector prediction (AMVP)mode, in accordance with some examples;

FIG. 3A is a conceptual diagram illustrating an example temporal motionvector predictor (TMVP) candidate, in accordance with some examples;

FIG. 3B is a conceptual diagram illustrating an example of motion vectorscaling, in accordance with some examples;

FIG. 4A is a conceptual diagram illustrating an example of neighboringsamples of a current coding unit used for estimating illuminationcompensation (IC) parameters for the current coding unit, in accordancewith some examples;

FIG. 4B is a conceptual diagram illustrating an example of neighboringsamples of a reference block used for estimating IC parameters for acurrent coding unit, in accordance with some examples;

FIG. 5A is a conceptual diagram illustrating an example of neighboringsamples of a current coding unit used for derivation of illuminationcompensation (IC) parameters for the current coding unit, in accordancewith some examples;

FIG. 5B is a conceptual diagram illustrating an example of neighboringsamples of a reference block used for derivation of IC parameters for acurrent coding unit, in accordance with some examples;

FIG. 6 is a conceptual diagram illustrating an example of overlappedblock motion compensation (OBMC), in accordance with some examples;

FIG. 7A is a conceptual diagram illustrating an example of OBMC forHEVC, in accordance with some examples;

FIG. 7B is another conceptual diagram illustrating the OBMC for HEVC, inaccordance with some examples;

FIG. 8A is a conceptual diagram illustrating an example of sub-blockswhere OBMC applies, in accordance with some examples;

FIG. 8B is a conceptual diagram illustrating an example ofsub-prediction units where OBMC applies, in accordance with someexamples;

FIG. 9 is a conceptual diagram illustrating an example of unilateralmotion estimation in frame rate up conversion (FRUC), in accordance withsome examples;

FIG. 10 is a conceptual diagram illustrating an example of bilateralmotion estimation in frame rate up conversion (FRUC), in accordance withsome examples;

FIG. 11A is a conceptual diagram illustrating an example of referencepictures used in template matching based decoder side motion vectorderivation (DMVD), in accordance with some examples;

FIG. 11B is a conceptual diagram illustrating an example of a currentpicture used in template matching based DMVD, in accordance with someexamples;

FIG. 12 is a conceptual diagram illustrating an example of mirror basedbi-directional motion vector derivation in DMVD, in accordance with someexamples;

FIG. 13 is a flowchart illustrating an example of decoding a predictionunit (PU) using DMVD, in accordance with some examples;

FIG. 14 is a conceptual diagram illustrating an example oftemplate-based derivation of local illumination compensation parameters,in accordance with some examples;

FIG. 15 is a flowchart illustrating an example of a process for improvedsignaling between an OBMC flag and an illumination compensation (IC)flag, in accordance with some examples;

FIG. 16 is a flowchart illustrating an example of a process ofprocessing video data, in accordance with some embodiments;

FIG. 17 is a flowchart illustrating another example of a process ofprocessing video data, in accordance with some embodiments;

FIG. 18 is a flowchart illustrating another example of a process ofprocessing video data, in accordance with some embodiments;

FIG. 19 is a block diagram illustrating an example video encodingdevice, in accordance with some examples;

FIG. 20 is a block diagram illustrating an example video decodingdevice, in accordance with some examples.

DETAILED DESCRIPTION

Certain aspects and embodiments of this disclosure are provided below.Some of these aspects and embodiments may be applied independently andsome of them may be applied in combination as would be apparent to thoseof skill in the art. In the following description, for the purposes ofexplanation, specific details are set forth in order to provide athorough understanding of embodiments of the invention. However, it willbe apparent that various embodiments may be practiced without thesespecific details. The figures and description are not intended to berestrictive.

The ensuing description provides exemplary embodiments only, and is notintended to limit the scope, applicability, or configuration of thedisclosure. Rather, the ensuing description of the exemplary embodimentswill provide those skilled in the art with an enabling description forimplementing an exemplary embodiment. It should be understood thatvarious changes may be made in the function and arrangement of elementswithout departing from the spirit and scope of the invention as setforth in the appended claims.

Specific details are given in the following description to provide athorough understanding of the embodiments. However, it will beunderstood by one of ordinary skill in the art that the embodiments maybe practiced without these specific details. For example, circuits,systems, networks, processes, and other components may be shown ascomponents in block diagram form in order not to obscure the embodimentsin unnecessary detail. In other instances, well-known circuits,processes, algorithms, structures, and techniques may be shown withoutunnecessary detail in order to avoid obscuring the embodiments.

Also, it is noted that individual embodiments may be described as aprocess which is depicted as a flowchart, a flow diagram, a data flowdiagram, a structure diagram, or a block diagram. Although a flowchartmay describe the operations as a sequential process, many of theoperations can be performed in parallel or concurrently. In addition,the order of the operations may be re-arranged. A process is terminatedwhen its operations are completed, but could have additional steps notincluded in a figure. A process may correspond to a method, a function,a procedure, a subroutine, a subprogram, etc. When a process correspondsto a function, its termination can correspond to a return of thefunction to the calling function or the main function.

The term “computer-readable medium” includes, but is not limited to,portable or non-portable storage devices, optical storage devices, andvarious other mediums capable of storing, containing, or carryinginstruction(s) and/or data. A computer-readable medium may include anon-transitory medium in which data can be stored and that does notinclude carrier waves and/or transitory electronic signals propagatingwirelessly or over wired connections. Examples of a non-transitorymedium may include, but are not limited to, a magnetic disk or tape,optical storage media such as compact disk (CD) or digital versatiledisk (DVD), flash memory, memory or memory devices. A computer-readablemedium may have stored thereon code and/or machine-executableinstructions that may represent a procedure, a function, a subprogram, aprogram, a routine, a subroutine, a module, a software package, a class,or any combination of instructions, data structures, or programstatements. A code segment may be coupled to another code segment or ahardware circuit by passing and/or receiving information, data,arguments, parameters, or memory contents. Information, arguments,parameters, data, etc. may be passed, forwarded, or transmitted via anysuitable means including memory sharing, message passing, token passing,network transmission, or the like.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middlewareor microcode, the program code or code segments to perform the necessarytasks (e.g., a computer-program product) may be stored in acomputer-readable or machine-readable medium. A processor(s) may performthe necessary tasks.

Video coding devices implement video compression techniques to encodeand decode video data efficiently. Video compression techniques mayinclude applying different prediction modes, including spatialprediction (e.g., intra-frame prediction or intra-prediction), temporalprediction (e.g., inter-frame prediction or inter-prediction),inter-layer prediction (across different layers of video data, and/orother prediction techniques to reduce or remove redundancy inherent invideo sequences. A video encoder can partition each picture of anoriginal video sequence into rectangular regions referred to as videoblocks or coding units (described in greater detail below). These videoblocks may be encoded using a particular prediction mode.

Video blocks may be divided in one or more ways into one or more groupsof smaller blocks. Blocks can include coding tree blocks, predictionblocks, transform blocks, or other suitable blocks. References generallyto a “block,” unless otherwise specified, may refer to such video blocks(e.g., coding tree blocks, coding blocks, prediction blocks, transformblocks, or other appropriate blocks or sub-blocks, as would beunderstood by one of ordinary skill. Further, each of these blocks mayalso interchangeably be referred to herein as “units” (e.g., coding treeunit (CTU), coding unit, prediction unit (PU), transform unit (TU), orthe like). In some cases, a unit may indicate a coding logical unit thatis encoded in a bitstream, while a block may indicate a portion of videoframe buffer a process is target to.

For inter-prediction modes, a video encoder can search for a blocksimilar to the block being encoded in a frame (or picture) located inanother temporal location, referred to as a reference frame or areference picture. The video encoder may restrict the search to acertain spatial displacement from the block to be encoded. A best matchmay be located using a two-dimensional (2D) motion vector that includesa horizontal displacement component and a vertical displacementcomponent. For intra-prediction modes, a video encoder may form thepredicted block using spatial prediction techniques based on data frompreviously encoded neighboring blocks within the same picture.

The video encoder may determine a prediction error. For example, theprediction can be determined as the difference between the pixel valuesin the block being encoded and the predicted block. The prediction errorcan also be referred to as the residual. The video encoder may alsoapply a transform to the prediction error (e.g., a discrete cosinetransform (DCT) or other suitable transform) to generate transformcoefficients. After transformation, the video encoder may quantize thetransform coefficients. The quantized transform coefficients and motionvectors may be represented using syntax elements, and, along withcontrol information, form a coded representation of a video sequence. Insome instances, the video encoder may entropy code syntax elements,thereby further reducing the number of bits needed for theirrepresentation.

A video decoder may, using the syntax elements and control informationdiscussed above, construct predictive data (e.g., a predictive block)for decoding a current frame. For example, the video decoder may add thepredicted block and the compressed prediction error. The video decodermay determine the compressed prediction error by weighting the transformbasis functions using the quantized coefficients. The difference betweenthe reconstructed frame and the original frame is called reconstructionerror.

In some examples, one or more systems and methods of processing videodata are directed to deriving or estimating illumination compensation(IC) parameters in block based video coding. In some instances, a videoencoder and/or a video decoder can perform local illuminationcompensation (LIC) (or illumination compensation (IC)) to efficientlycode variations in illumination (e.g., brightness) between one or morepictures. The video encoder and/or the video decoder can determine oneor more IC parameters (e.g., an offset, one or more scaling factors, ashift number, or other suitable IC parameters) for the coding block orcoding unit being encoded or decoded. The IC parameters can bedetermined based on samples of multiple reference blocks, samples of oneor more neighboring blocks of the current block, and/or otherinformation. The video decoder can utilize the IC parameters and/orother data to construct predictive data for decoding the current block.

In some examples, one or more systems and methods of processing videodata are directed to adaptively determining the size of one or moretemplates to use for LIC. For example, the number of rows and/or columnof pixels in a template used to derive one or more LIC parameters for acurrent block can vary depending on a parameter of the current block.The parameter can include the block size (e.g., the width, the height,or the width and height of the block, or other suitable measure ofsize), a chroma format of the block (e.g., 4:2:0 format, 4:2:2 format,4:4:4 format, or other suitable chroma format), or other parameter thatcan be used to determine the template size.

In some examples, one or more systems and methods of processing videodata are directed to adaptive selection of weights from a pre-definedset of weights. For example, a template-based solution can be used tosearch for one more optimal weights out of the pre-defined set ofweights without having to signal the choice of weights to the decoder.Such systems and methods can be used for any matching based motionprediction or compensation that utilizes weights in the predictionprocess. For example, such systems and methods can be used for anybi-predicted block where two motion vectors pointing to two logicallyseparate pictures are considered. In such examples, the weights can bereferred to as a pair of weighting factors for both reference pictures(e.g., ref0 and ref1) with a sum equal to one. Examples of matchingbased motion prediction or compensation techniques that such systems andmethods can be used for include LIC, weighted prediction (WP), or anyother suitable techniques that utilize weights in the predictionprocess.

The techniques described herein can be applied to any of the existingvideo codecs (e.g., High Efficiency Video Coding (HEVC), Advanced VideoCoding (AVC), or other suitable existing video codec), or can be anefficient coding tool for any future video coding standards, such as,for example, the joint exploration model (JEM).

FIG. 1 is a block diagram illustrating an example of a system 100including an encoding device 104 and a decoding device 112. The encodingdevice 104 may be part of a source device, and the decoding device 112may be part of a receiving device. The source device and/or thereceiving device may include an electronic device, such as a mobile orstationary telephone handset (e.g., smartphone, cellular telephone, orthe like), a desktop computer, a laptop or notebook computer, a tabletcomputer, a set-top box, a television, a camera, a display device, adigital media player, a video gaming console, a video streaming device,an Internet Protocol (IP) camera, or any other suitable electronicdevice. In some examples, the source device and the receiving device mayinclude one or more wireless transceivers for wireless communications.The coding techniques described herein are applicable to video coding invarious multimedia applications, including streaming video transmissions(e.g., over the Internet), television broadcasts or transmissions,encoding of digital video for storage on a data storage medium, decodingof digital video stored on a data storage medium, or other applications.In some examples, system 100 can support one-way or two-way videotransmission to support applications such as video conferencing, videostreaming, video playback, video broadcasting, gaming, and/or videotelephony.

The encoding device 104 (or encoder) can be used to encode video datausing a video coding standard or protocol to generate an encoded videobitstream. Examples of video coding standards include ITU-T H.261,ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-TH.263, ISO/IEC MPEG-4 Visual, ITU-T H.264 (also known as ISO/IEC MPEG-4AVC), including its Scalable Video Coding (SVC) and Multiview VideoCoding (MVC) extensions, and High Efficiency Video Coding (HEVC) orITU-T H.265. Various extensions to HEVC deal with multi-layer videocoding exist, including the range and screen content coding extensions,3D video coding (3D-HEVC) and multiview extensions (MV-HEVC) andscalable extension (SHVC). The HEVC and its extensions has beendeveloped by the Joint Collaboration Team on Video Coding (JCT-VC) aswell as Joint Collaboration Team on 3D Video Coding ExtensionDevelopment (JCT-3V) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG). MPEG and ITU-T VCEG havealso formed a joint exploration video team (WET) to explore new codingtools for the next generation of video coding standard. The referencesoftware is called JEM (joint exploration model).

Many embodiments described herein provide examples using the JEM model,the HEVC standard, and/or extensions thereof. However, the techniquesand systems described herein may also be applicable to other codingstandards, such as AVC, MPEG, extensions thereof, or other suitablecoding standards already available or not yet available or developed.Accordingly, while the techniques and systems described herein may bedescribed with reference to a particular video coding standard, one ofordinary skill in the art will appreciate that the description shouldnot be interpreted to apply only to that particular standard.

Referring to FIG. 1, a video source 102 may provide the video data tothe encoding device 104. The video source 102 may be part of the sourcedevice, or may be part of a device other than the source device. Thevideo source 102 may include a video capture device (e.g., a videocamera, a camera phone, a video phone, or the like), a video archivecontaining stored video, a video server or content provider providingvideo data, a video feed interface receiving video from a video serveror content provider, a computer graphics system for generating computergraphics video data, a combination of such sources, or any othersuitable video source.

The video data from the video source 102 may include one or more inputpictures or frames. A picture or frame is a still image that is part ofa video. The encoder engine 106 (or encoder) of the encoding device 104encodes the video data to generate an encoded video bitstream. In someexamples, an encoded video bitstream (or “video bitstream” or“bitstream”) is a series of one or more coded video sequences. A codedvideo sequence (CVS) includes a series of access units (AUs) startingwith an AU that has a random access point picture in the base layer andwith certain properties up to and not including a next AU that has arandom access point picture in the base layer and with certainproperties. For example, the certain properties of a random access pointpicture that starts a CVS may include a RASL flag (e.g.,NoRaslOutputFlag) equal to 1. Otherwise, a random access point picture(with RASL flag equal to 0) does not start a CVS. An access unit (AU)includes one or more coded pictures and control informationcorresponding to the coded pictures that share the same output time.Coded slices of pictures are encapsulated in the bitstream level intodata units called network abstraction layer (NAL) units. For example, anHEVC video bitstream may include one or more CVSs including NAL units.Each of the NAL units has a NAL unit header. In one example, the headeris one-byte for H.264/AVC (except for multi-layer extensions) andtwo-byte for HEVC. The syntax elements in the NAL unit header take thedesignated bits and therefore are visible to all kinds of systems andtransport layers, such as Transport Stream, Real-time Transport (RTP)Protocol, File Format, among others.

Two classes of NAL units exist in the HEVC standard, including videocoding layer (VCL) NAL units and non-VCL NAL units. A VCL NAL unitincludes one slice or slice segment (described below) of coded picturedata, and a non-VCL NAL unit includes control information that relatesto one or more coded pictures. In some cases, a NAL unit can be referredto as a packet. An HEVC AU includes VCL NAL units containing codedpicture data and non-VCL NAL units (if any) corresponding to the codedpicture data.

NAL units may contain a sequence of bits forming a coded representationof the video data (e.g., an encoded video bitstream, a CVS of abitstream, or the like), such as coded representations of pictures in avideo. The encoder engine 106 generates coded representations ofpictures by partitioning each picture into multiple slices. A slice isindependent of other slices so that information in the slice is codedwithout dependency on data from other slices within the same picture. Aslice includes one or more slice segments including an independent slicesegment and, if present, one or more dependent slice segments thatdepend on previous slice segments. The slices are then partitioned intocoding tree blocks (CTBs) of luma samples and chroma samples. A CTB ofluma samples and one or more CTBs of chroma samples, along with syntaxfor the samples, are referred to as a coding tree unit (CTU). A CTU isthe basic processing unit for HEVC encoding. A CTU can be split intomultiple coding units (CUs) of varying sizes. A CU contains luma andchroma sample arrays that are referred to as coding blocks (CBs).

The luma and chroma CBs can be further split into prediction blocks(PBs). A PB is a block of samples of the luma component or a chromacomponent that uses the same motion parameters for inter-prediction orintra-block copy prediction (when available or enabled for use). Theluma PB and one or more chroma PBs, together with associated syntax,form a prediction unit (PU). For inter-prediction, a set of motionparameters (e.g., one or more motion vectors, reference indices, or thelike) is signaled in the bitstream for each PU and is used forinter-prediction of the luma PB and the one or more chroma PBs. Themotion parameters can also be referred to as motion information. A CBcan also be partitioned into one or more transform blocks (TBs). A TBrepresents a square block of samples of a color component on which thesame two-dimensional transform is applied for coding a predictionresidual signal. A transform unit (TU) represents the TBs of luma andchroma samples, and corresponding syntax elements.

A size of a CU corresponds to a size of the coding mode and may besquare in shape. For example, a size of a CU may be 8×8 samples, 16×16samples, 32×32 samples, 64×64 samples, or any other appropriate size upto the size of the corresponding CTU. The phrase “N×N” is used herein torefer to pixel dimensions of a video block in terms of vertical andhorizontal dimensions (e.g., 8 pixels×8 pixels). The pixels in a blockmay be arranged in rows and columns. In some embodiments, blocks may nothave the same number of pixels in a horizontal direction as in avertical direction. Syntax data associated with a CU may describe, forexample, partitioning of the CU into one or more PUs. Partitioning modesmay differ between whether the CU is intra-prediction mode encoded orinter-prediction mode encoded. PUs may be partitioned to be non-squarein shape. Syntax data associated with a CU may also describe, forexample, partitioning of the CU into one or more TUs according to a CTU.A TU can be square or non-square in shape.

According to the HEVC standard, transformations may be performed usingtransform units (TUs). TUs may vary for different CUs. The TUs may besized based on the size of PUs within a given CU. The TUs may be thesame size or smaller than the PUs. In some examples, residual samplescorresponding to a CU may be subdivided into smaller units using aquadtree structure known as residual quad tree (RQT). Leaf nodes of theRQT may correspond to TUs. Pixel difference values associated with theTUs may be transformed to produce transform coefficients. The transformcoefficients may then be quantized by the encoder engine 106.

Once the pictures of the video data are partitioned into CUs, theencoder engine 106 predicts each PU using a prediction mode. Theprediction unit or prediction block is then subtracted from the originalvideo data to get residuals (described below). For each CU, a predictionmode may be signaled inside the bitstream using syntax data. Aprediction mode may include intra-prediction (or intra-pictureprediction) or inter-prediction (or inter-picture prediction).Intra-prediction utilizes the correlation between spatially neighboringsamples within a picture. For example, using intra-prediction, each PUis predicted from neighboring image data in the same picture using, forexample, DC prediction to find an average value for the PU, planarprediction to fit a planar surface to the PU, direction prediction toextrapolate from neighboring data, or any other suitable types ofprediction. Inter-prediction uses the temporal correlation betweenpictures in order to derive a motion-compensated prediction for a blockof image samples. For example, using inter-prediction, each PU ispredicted using motion compensation prediction from image data in one ormore reference pictures (before or after the current picture in outputorder). The decision whether to code a picture area using inter-pictureor intra-picture prediction may be made, for example, at the CU level.

In some examples, the one or more slices of a picture are assigned aslice type. Slice types include an I slice, a P slice, and a B slice. AnI slice (intra-frames, independently decodable) is a slice of a picturethat is only coded by intra-prediction, and therefore is independentlydecodable since the I slice requires only the data within the frame topredict any prediction unit or prediction block of the slice. A P slice(uni-directional predicted frames) is a slice of a picture that may becoded with intra-prediction and with uni-directional inter-prediction.Each prediction unit or prediction block within a P slice is eithercoded with Intra prediction or inter-prediction. When theinter-prediction applies, the prediction unit or prediction block isonly predicted by one reference picture, and therefore reference samplesare only from one reference region of one frame. A B slice(bi-directional predictive frames) is a slice of a picture that may becoded with intra-prediction and with inter-prediction (e.g., eitherbi-prediction or uni-prediction). A prediction unit or prediction blockof a B slice may be bi-directionally predicted from two referencepictures, where each picture contributes one reference region and samplesets of the two reference regions are weighted (e.g., with equal weightsor with different weights) to produce the prediction signal of thebi-directional predicted block. As explained above, slices of onepicture are independently coded. In some cases, a picture can be codedas just one slice.

A PU may include the data (e.g., motion parameters or other suitabledata) related to the prediction process. For example, when the PU isencoded using intra-prediction, the PU may include data describing anintra-prediction mode for the PU. As another example, when the PU isencoded using inter-prediction, the PU may include data defining amotion vector for the PU. The data defining the motion vector for a PUmay describe, for example, a horizontal component of the motion vector(Δx), a vertical component of the motion vector (Δy), a resolution forthe motion vector (e.g., integer precision, one-quarter pixel precisionor one-eighth pixel precision), a reference picture to which the motionvector points, a reference index, a reference picture list (e.g., List0, List 1, or List C) for the motion vector, or any combination thereof.

The encoding device 104 may then perform transformation andquantization. For example, following prediction, the encoder engine 106may calculate residual values corresponding to the PU. Residual valuesmay comprise pixel difference values between the current block of pixelsbeing coded (the PU) and the prediction block used to predict thecurrent block (e.g., the predicted version of the current block). Forexample, after generating a prediction block (e.g., issuinginter-prediction or intra-prediction), the encoder engine 106 cangenerate a residual block by subtracting the prediction block producedby a prediction unit from the current block. The residual block includesa set of pixel difference values that quantify differences between pixelvalues of the current block and pixel values of the prediction block. Insome examples, the residual block may be represented in atwo-dimensional block format (e.g., a two-dimensional matrix or array ofpixel values). In such examples, the residual block is a two-dimensionalrepresentation of the pixel values.

Any residual data that may be remaining after prediction is performed istransformed using a block transform, which may be based on discretecosine transform, discrete sine transform, an integer transform, awavelet transform, other suitable transform function, or any combinationthereof. In some cases, one or more block transforms (e.g., sizes 32×32,16×16, 8×8, 4×4, or other suitable size) may be applied to residual datain each CU. In some embodiments, a TU may be used for the transform andquantization processes implemented by the encoder engine 106. A given CUhaving one or more PUs may also include one or more TUs. As described infurther detail below, the residual values may be transformed intotransform coefficients using the block transforms, and then may bequantized and scanned using TUs to produce serialized transformcoefficients for entropy coding.

In some embodiments following intra-predictive or inter-predictivecoding using PUs of a CU, the encoder engine 106 may calculate residualdata for the TUs of the CU. The PUs may comprise pixel data in thespatial domain (or pixel domain). The TUs may comprise coefficients inthe transform domain following application of a block transform. Aspreviously noted, the residual data may correspond to pixel differencevalues between pixels of the unencoded picture and prediction valuescorresponding to the PUs. Encoder engine 106 may form the TUs includingthe residual data for the CU, and may then transform the TUs to producetransform coefficients for the CU.

The encoder engine 106 may perform quantization of the transformcoefficients. Quantization provides further compression by quantizingthe transform coefficients to reduce the amount of data used torepresent the coefficients. For example, quantization may reduce the bitdepth associated with some or all of the coefficients. In one example, acoefficient with an n-bit value may be rounded down to an m-bit valueduring quantization, with n being greater than m.

Once quantization is performed, the coded video bitstream includesquantized transform coefficients, prediction information (e.g.,prediction modes, motion vectors, block vectors, or the like),partitioning information, and any other suitable data, such as othersyntax data. The different elements of the coded video bitstream maythen be entropy encoded by the encoder engine 106. In some examples, theencoder engine 106 may utilize a predefined scan order to scan thequantized transform coefficients to produce a serialized vector that canbe entropy encoded. In some examples, encoder engine 106 may perform anadaptive scan. After scanning the quantized transform coefficients toform a vector (e.g., a one-dimensional vector), the encoder engine 106may entropy encode the vector. For example, the encoder engine 106 mayuse context adaptive variable length coding, context adaptive binaryarithmetic coding, syntax-based context-adaptive binary arithmeticcoding, probability interval partitioning entropy coding, or anothersuitable entropy encoding technique.

As previously described, an HEVC bitstream includes a group of NALunits, including VCL NAL units and non-VCL NAL units. VCL NAL unitsinclude coded picture data forming a coded video bitstream. For example,a sequence of bits forming the coded video bitstream is present in VCLNAL units. Non-VCL NAL units may contain parameter sets with high-levelinformation relating to the encoded video bitstream, in addition toother information. For example, a parameter set may include a videoparameter set (VPS), a sequence parameter set (SPS), and a pictureparameter set (PPS). Examples of goals of the parameter sets include bitrate efficiency, error resiliency, and providing systems layerinterfaces. Each slice references a single active PPS, SPS, and VPS toaccess information that the decoding device 112 may use for decoding theslice. An identifier (ID) may be coded for each parameter set, includinga VPS ID, an SPS ID, and a PPS ID. An SPS includes an SPS ID and a VPSID. A PPS includes a PPS ID and an SPS ID. Each slice header includes aPPS ID. Using the IDs, active parameter sets can be identified for agiven slice.

A PPS includes information that applies to all slices in a givenpicture. Because of this, all slices in a picture refer to the same PPS.Slices in different pictures may also refer to the same PPS. An SPSincludes information that applies to all pictures in a same coded videosequence (CVS) or bitstream. As previously described, a coded videosequence is a series of access units (AUs) that starts with a randomaccess point picture (e.g., an instantaneous decode reference (IDR)picture or broken link access (BLA) picture, or other appropriate randomaccess point picture) in the base layer and with certain properties(described above) up to and not including a next AU that has a randomaccess point picture in the base layer and with certain properties (orthe end of the bitstream). The information in an SPS may not change frompicture to picture within a coded video sequence. Pictures in a codedvideo sequence may use the same SPS. The VPS includes information thatapplies to all layers within a coded video sequence or bitstream. TheVPS includes a syntax structure with syntax elements that apply toentire coded video sequences. In some embodiments, the VPS, SPS, or PPSmay be transmitted in-band with the encoded bitstream. In someembodiments, the VPS, SPS, or PPS may be transmitted out-of-band in aseparate transmission than the NAL units containing coded video data.

A video bitstream can also include Supplemental Enhancement Information(SEI) messages. For example, an SEI NAL unit can be part of the videobitstream. In some cases, an SEI message can contain information that isnot needed by the decoding process. For example, the information in anSEI message may not be essential for the decoder to decode the videopictures of the bitstream, but the decoder can be use the information toimprove the display or processing of the pictures (e.g., the decodedoutput). The information in an SEI message can be embedded metadata. Inone illustrative example, the information in an SEI message could beused by decoder-side entities to improve the viewability of the content.In some instances, certain application standards may mandate thepresence of such SEI messages in the bitstream so that the improvementin quality can be brought to all devices that conform to the applicationstandard (e.g., the carriage of the frame-packing SEI message forframe-compatible plano-stereoscopic 3DTV video format, where the SEImessage is carried for every frame of the video, handling of a recoverypoint SEI message, use of pan-scan scan rectangle SEI message in DVB, inaddition to many other examples).

The output 110 of the encoding device 104 may send the NAL units makingup the encoded video bitstream data over the communications link 120 tothe decoding device 112 of the receiving device. The input 114 of thedecoding device 112 may receive the NAL units. The communications link120 may include a channel provided by a wireless network, a wirednetwork, or a combination of a wired and wireless network. A wirelessnetwork may include any wireless interface or combination of wirelessinterfaces and may include any suitable wireless network (e.g., theInternet or other wide area network, a packet-based network, WiFi™,radio frequency (RF), UWB, WiFi-Direct, cellular, Long-Term Evolution(LTE), WiMax™, or the like). A wired network may include any wiredinterface (e.g., fiber, ethernet, powerline ethernet, ethernet overcoaxial cable, digital signal line (DSL), or the like). The wired and/orwireless networks may be implemented using various equipment, such asbase stations, routers, access points, bridges, gateways, switches, orthe like. The encoded video bitstream data may be modulated according toa communication standard, such as a wireless communication protocol, andtransmitted to the receiving device.

In some examples, the encoding device 104 may store encoded videobitstream data in storage 108. The output 110 may retrieve the encodedvideo bitstream data from the encoder engine 106 or from the storage108. Storage 108 may include any of a variety of distributed or locallyaccessed data storage media. For example, the storage 108 may include ahard drive, a storage disc, flash memory, volatile or non-volatilememory, or any other suitable digital storage media for storing encodedvideo data.

The input 114 of the decoding device 112 receives the encoded videobitstream data and may provide the video bitstream data to the decoderengine 116, or to storage 118 for later use by the decoder engine 116.The decoder engine 116 may decode the encoded video bitstream data byentropy decoding (e.g., using an entropy decoder) and extracting theelements of one or more coded video sequences making up the encodedvideo data. The decoder engine 116 may then rescale and perform aninverse transform on the encoded video bitstream data. Residual data isthen passed to a prediction stage of the decoder engine 116. The decoderengine 116 then predicts a block of pixels (e.g., a PU). In someexamples, the prediction is added to the output of the inverse transform(the residual data).

The decoding device 112 may output the decoded video to a videodestination device 122, which may include a display or other outputdevice for displaying the decoded video data to a consumer of thecontent. In some aspects, the video destination device 122 may be partof the receiving device that includes the decoding device 112. In someaspects, the video destination device 122 may be part of a separatedevice other than the receiving device.

In some embodiments, the video encoding device 104 and/or the videodecoding device 112 may be integrated with an audio encoding device andaudio decoding device, respectively. The video encoding device 104and/or the video decoding device 112 may also include other hardware orsoftware that is necessary to implement the coding techniques describedabove, such as one or more microprocessors, digital signal processors(DSPs), application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), discrete logic, software, hardware,firmware or any combinations thereof. The video encoding device 104 andthe video decoding device 112 may be integrated as part of a combinedencoder/decoder (codec) in a respective device. An example of specificdetails of the encoding device 104 is described below with reference toFIG. 19. An example of specific details of the decoding device 112 isdescribed below with reference to FIG. 20.

Extensions to the HEVC standard include the Multiview Video Codingextension, referred to as MV-HEVC, and the Scalable Video Codingextension, referred to as SHVC. The MV-HEVC and SHVC extensions sharethe concept of layered coding, with different layers being included inthe encoded video bitstream. Each layer in a coded video sequence isaddressed by a unique layer identifier (ID). A layer ID may be presentin a header of a NAL unit to identify a layer with which the NAL unit isassociated. In MV-HEVC, different layers can represent different viewsof the same scene in the video bitstream. In SHVC, different scalablelayers are provided that represent the video bitstream in differentspatial resolutions (or picture resolution) or in differentreconstruction fidelities. The scalable layers may include a base layer(with layer ID=0) and one or more enhancement layers (with layer IDs=1,2, . . . n). The base layer may conform to a profile of the firstversion of HEVC, and represents the lowest available layer in abitstream. The enhancement layers have increased spatial resolution,temporal resolution or frame rate, and/or reconstruction fidelity (orquality) as compared to the base layer. The enhancement layers arehierarchically organized and may (or may not) depend on lower layers. Insome examples, the different layers may be coded using a single standardcodec (e.g., all layers are encoded using HEVC, SHVC, or other codingstandard). In some examples, different layers may be coded using amulti-standard codec. For example, a base layer may be coded using AVC,while one or more enhancement layers may be coded using SHVC and/orMV-HEVC extensions to the HEVC standard.

In general, a layer includes a set of VCL NAL units and a correspondingset of non-VCL NAL units. The NAL units are assigned a particular layerID value. Layers can be hierarchical in the sense that a layer maydepend on a lower layer. A layer set refers to a set of layersrepresented within a bitstream that are self-contained, meaning that thelayers within a layer set can depend on other layers in the layer set inthe decoding process, but do not depend on any other layers fordecoding. Accordingly, the layers in a layer set can form an independentbitstream that can represent video content. The set of layers in a layerset may be obtained from another bitstream by operation of asub-bitstream extraction process. A layer set may correspond to the setof layers that is to be decoded when a decoder wants to operateaccording to certain parameters.

As described above, for each block, a set of motion information (alsoreferred to herein as motion parameters) can be available. A set ofmotion information contains motion information for forward and backwardprediction directions. The forward and backward prediction directionsare two prediction directions of a bi-directional prediction mode, inwhich case the terms “forward” and “backward” do not necessarily have ageometrical meaning. Instead, “forward” and “backward” correspond toreference picture list 0 (RefPicList0) and reference picture list 1(RefPicList1) of a current picture. In some examples, when only onereference picture list is available for a picture or slice, onlyRefPicList0 is available and the motion information of each block of aslice is always forward.

In some cases, a motion vector together with its reference index is usedin coding processes (e.g., motion compensation). Such a motion vectorwith the associated reference index is denoted as a uni-predictive setof motion information. For each prediction direction, the motioninformation can contain a reference index and a motion vector. In somecases, for simplicity, a motion vector itself may be referred in a waythat it is assumed that it has an associated reference index. Areference index is used to identify a reference picture in the currentreference picture list (RefPicList0 or RefPicList1). A motion vector hasa horizontal and a vertical component that provide an offset from thecoordinate position in the current picture to the coordinates in thereference picture identified by the reference index. For example, areference index can indicate a particular reference picture that shouldbe used for a block in a current picture, and the motion vector canindicate where in the reference picture the best-matched block (theblock that best matches the current block) is in the reference picture.

A picture order count (POC) can be used in video coding standards toidentify a display order of a picture. Although there are cases forwhich two pictures within one coded video sequence may have the same POCvalue, it typically does not happen within a coded video sequence. Whenmultiple coded video sequences are present in a bitstream, pictures witha same value of POC may be closer to each other in terms of decodingorder. POC values of pictures can be used for reference picture listconstruction, derivation of reference picture set as in HEVC, and motionvector scaling.

In H.264/AVC, each inter macroblock (MB) may be partitioned in fourdifferent ways, including: one 16×16 MB partition; two 16×8 MBpartitions; two 8×16 MB partitions; and four 8×8 MB partitions.Different MB partitions in one MB may have different reference indexvalues for each direction (RefPicList0 or RefPicList1). In some cases,when an MB is not partitioned into four 8×8 MB partitions, it can haveonly one motion vector for each MB partition in each direction. In somecases, when an MB is partitioned into four 8×8 MB partitions, each 8×8MB partition can be further partitioned into sub-blocks, in which caseeach sub-block can have a different motion vector in each direction. Insome examples, there are four different ways to get sub-blocks from an8×8 MB partition, including: one 8×8 sub-block; two 8×4 sub-blocks; two4×8 sub-blocks; and four 4×4 sub-blocks. Each sub-block can have adifferent motion vector in each direction. Therefore, a motion vector ispresent in a level equal to higher than sub-block.

In AVC, a temporal direct mode can be enabled at either the MB level orthe MB partition level for skip and/or direct mode in B slices. For eachMB partition, the motion vectors of the block co-located with thecurrent MB partition in the RefPicList1[0] of the current block are usedto derive the motion vectors. Each motion vector in the co-located blockis scaled based on POC distances.

A spatial direct mode can also be performed in AVC. For example, in AVC,a direct mode can also predict motion information from the spatialneighbors.

In HEVC, the largest coding unit in a slice is called a coding treeblock (CTB). A CTB contains a quad-tree, the nodes of which are codingunits. The size of a CTB can range from 16×16 to 64×64 in the HEVC mainprofile. In some cases, 8×8 CTB sizes can be supported. A coding unit(CU) could be the same size of a CTB and as small as 8×8. In some cases,each coding unit is coded with one mode. When a CU is inter-coded, theCU may be further partitioned into 2 or 4 prediction units (PUs), or maybecome just one PU when further partition does not apply. When two PUsare present in one CU, they can be half size rectangles or tworectangles with ¼ or ¾ size of the CU.

When the CU is inter-coded, one set of motion information is present foreach PU. In addition, each PU is coded with a unique inter-predictionmode to derive the set of motion information.

For motion prediction in HEVC, there are two inter-prediction modes,including merge mode and advanced motion vector prediction (AMVP) modefor a prediction unit (PU). Skip is considered as a special case ofmerge. In either AMVP or merge mode, a motion vector (MV) candidate listis maintained for multiple motion vector predictors. The motionvector(s), as well as reference indices in the merge mode, of thecurrent PU are generated by taking one candidate from the MV candidatelist.

In some examples, the MV candidate list contains up to five candidatesfor the merge mode and two candidates for the AMVP mode. In otherexamples, different numbers of candidates can be included in a MVcandidate list for merge mode and/or AMVP mode. A merge candidate maycontain a set of motion information. For example, a set of motioninformation can include motion vectors corresponding to both referencepicture lists (list 0 and list 1) and the reference indices. If a mergecandidate is identified by a merge index, the reference pictures areused for the prediction of the current blocks, as well as the associatedmotion vectors are determined. However, under AMVP mode, for eachpotential prediction direction from either list 0 or list 1, a referenceindex needs to be explicitly signaled, together with an MVP index to theMV candidate list since the AMVP candidate contains only a motionvector. In AMVP mode, the predicted motion vectors can be furtherrefined.

As can be seen above, a merge candidate corresponds to a full set ofmotion information, while an AMVP candidate contains just one motionvector for a specific prediction direction and reference index. Thecandidates for both modes are derived similarly from the same spatialand temporal neighboring blocks.

In some examples, merge mode allows an inter-predicted PU to inherit thesame motion vector or vectors, prediction direction, and referencepicture index or indices from an inter-predicted PU that includes amotion data position selected from a group of spatially neighboringmotion data positions and one of two temporally co-located motion datapositions. For AMVP mode, motion vector or vectors of a PU can bepredicatively coded relative to one or more motion vector predictors(MVPs) from an AMVP candidate list constructed by an encoder. In someinstances, for single direction inter-prediction of a PU, the encodercan generate a single AMVP candidate list. In some instances, forbi-directional prediction of a PU, the encoder can generate two AMVPcandidate lists, one using motion data of spatial and temporalneighboring PUs from the forward prediction direction and one usingmotion data of spatial and temporal neighboring PUs from the backwardprediction direction.

The candidates for both modes can be derived from spatial and/ortemporal neighboring blocks. For example, FIG. 2A and FIG. 2B includeconceptual diagrams illustrating spatial neighboring candidates in HEVC.FIG. 2A illustrates spatial neighboring motion vector (MV) candidatesfor merge mode. FIG. 2B illustrates spatial neighboring motion vector(MV) candidates for AMVP mode. Spatial MV candidates are derived fromthe neighboring blocks for a specific PU (PU0), although the methodsgenerating the candidates from the blocks differ for merge and AMVPmodes.

In merge mode, the encoder can form a merging candidate list byconsidering merging candidates from various motion data positions. Forexample, as shown in FIG. 2A, up to four spatial MV candidates can bederived with respect spatially neighboring motion data positions shownwith numbers 0-4 in FIG. 2A. The MV candidates can be ordered in themerging candidate list in the order shown by the numbers 0-4. Forexample, the positions and order can include: left position (0), aboveposition (1), above right position (2), below left position (3), andabove left position (4).

In AVMP mode shown in FIG. 2B, the neighboring blocks are divided intotwo groups: left group including the blocks 0 and 1, and above groupincluding the blocks 2, 3, and 4. For each group, the potentialcandidate in a neighboring block referring to the same reference pictureas that indicated by the signaled reference index has the highestpriority to be chosen to form a final candidate of the group. It ispossible that all neighboring blocks do not contain a motion vectorpointing to the same reference picture. Therefore, if such a candidatecannot be found, the first available candidate will be scaled to formthe final candidate, thus the temporal distance differences can becompensated.

FIG. 3A and FIG. 3B include conceptual diagrams illustrating temporalmotion vector prediction in HEVC. A temporal motion vector predictor(TMVP) candidate, if enabled and available, is added into a MV candidatelist after spatial motion vector candidates. The process of motionvector derivation for a TMVP candidate is the same for both merge andAMVP modes. In some instances, however, the target reference index forthe TMVP candidate in the merge mode can be set to zero or can bederived from that of the neighboring blocks.

The primary block location for TMVP candidate derivation is the bottomright block outside of the collocated PU, as shown in FIG. 3A as a block“T”, to compensate for the bias to the above and left blocks used togenerate spatial neighboring candidates. However, if that block islocated outside of the current CTB (or LCU) row or motion information isnot available, the block is substituted with a center block of the PU. Amotion vector for a TMVP candidate is derived from the co-located PU ofthe co-located picture, indicated in the slice level. Similar totemporal direct mode in AVC, a motion vector of the TMVP candidate maybe subject to motion vector scaling, which is performed to compensatefor distance differences.

Other aspects of motion prediction are covered in the HEVC standard. Forexample, several other aspects of merge and AMVP modes are covered. Oneaspect includes motion vector scaling. With respect to motion vectorscaling, it can be assumed that the value of motion vectors isproportional to the distance of pictures in the presentation time. Amotion vector associates two pictures—the reference picture and thepicture containing the motion vector (namely the containing picture).When a motion vector is utilized to predict the other motion vector, thedistance of the containing picture and the reference picture iscalculated based on the Picture Order Count (POC) values.

For a motion vector to be predicted, both its associated containingpicture and reference picture may be different. Therefore, a newdistance (based on POC) is calculated. And, the motion vector is scaledbased on these two POC distances. For a spatial neighboring candidate,the containing pictures for the two motion vectors are the same, whilethe reference pictures are different. In HEVC, motion vector scalingapplies to both TMVP and AMVP for spatial and temporal neighboringcandidates.

Another aspect of motion prediction includes artificial motion vectorcandidate generation. For example, if a motion vector candidate list isnot complete, artificial motion vector candidates are generated andinserted at the end of the list until all candidates are obtained. Inmerge mode, there are two types of artificial MV candidates: combinedcandidate derived only for B-slices; and zero candidates used only forAMVP if the first type does not provide enough artificial candidates.For each pair of candidates that are already in the candidate list andthat have necessary motion information, bi-directional combined motionvector candidates are derived by a combination of the motion vector ofthe first candidate referring to a picture in the list 0 and the motionvector of a second candidate referring to a picture in the list 1.

Another aspect of merge and AMVP modes includes a pruning process forcandidate insertion. For example, candidates from different blocks mayhappen to be the same, which decreases the efficiency of a merge and/orAMVP candidate list. A pruning process can be applied to solve thisproblem. The pruning process compares one candidate against the othersin the current candidate list to avoid inserting identical candidate incertain extent. To reduce the complexity, only limited numbers ofpruning process is applied instead of comparing each potential one withall the other existing ones.

There are various related motion-prediction technologies. One predictiontechnology is local illumination compensation (LIC). Illuminationcompensation has been proposed for HEVC. For example, in JCTVC-0041,Partition Based Illumination Compensation (PBIC) was proposed. Differentfrom weighted prediction (WP), which enables and/or disables WP, andsignals WP parameters at the slice level (as described below), PBICenables and/or disables illumination compensation (IC) and signals ICparameters at the prediction unit (PU) level to handle localillumination variation. In JVET-B0023, the block-based LIC is extendedto the CU, similar to PU in HEVC, CU becomes the basic unit whichcarries the motion information in the QTBT structure.

Similar to Weighted Prediction (WP), which is described in more detailbelow, a scaling factor (also denoted by a) and an offset (also denotedby b) is used in IC, and the shift number is fixed to be 6. An IC flagis coded for each PU to indicate whether IC applies for current PU ornot. If IC applies for the PU, a set of IC parameters (e.g., a and b)are signaled to the decoder and is used for motion compensation. In someexamples, to save bits spent on IC parameters, the chroma componentshares the scaling factors with luma component and a fixed offset 128 isused.

In 3D-HEVC, IC is enabled for inter-view prediction. Different from WPand PBIC, which signals IC parameters explicitly, it derives ICparameters based on neighboring samples of current CU and neighboringsamples of reference block. IC applies to 2N×2N partition mode only. ForAMVP mode, one IC flag is signaled for each CU that is predicted from aninter-view reference picture. For merge mode, to save bits, an IC flagis signaled only when the merge index of the PU is not equal to 0. Insome cases, IC does not apply to CU that is only predicted from temporalreference pictures.

With respect to derivation of IC parameters, the linear IC model used ininter-view prediction is shown in Equation (1):

p(i,j)=a*r(i+dv _(x) ,j+dv _(y))+b, where (i,j)εPU_(c)  Equation (1)

Here, PU_(c) is the current PU, (i, j) is the coordinate of pixels inPU_(c), (dv_(x), dv_(y)) is the disparity vector of PU_(c). p(i, j) isthe prediction of PU_(c), r is the PU's reference picture from theneighboring view, and a and b are parameters of the linear IC model.

To estimate parameter a and b for a PU, two sets of pixels, as shown inFIG. 4A and FIG. 4B are used. The first set of pixels are shown in FIG.4A and include available reconstructed neighboring pixels in a leftcolumn and an above row of the current CU (the CU that contains thecurrent PU). The second set of pixels are shown in FIG. 4B and includecorresponding neighboring pixels of the current CU's reference block.The reference block of the current CU is found by using the current PU'sdisparity vector.

Let Rec_(new) and Rec_(refneig) denote used neighboring pixel set of thecurrent CU and its reference block, respectively, and let 2N denote thepixel number in Rec_(neig) and Rec_(refneig). Then, a and b can becalculated as:

$\begin{matrix}{a = \frac{\begin{matrix}{{2{N \cdot {\sum\limits_{i = 0}^{{2N} - 1}\; {{{{Rec}_{neig}(i)} \cdot {Rec}_{refneig}}(i)}}}} -} \\{\sum\limits_{i = 0}^{{2N} - 1}\; {{{Rec}_{neig}(i)} \cdot {\sum\limits_{i = 0}^{{2N} - 1}\; {{Rec}_{refneig}(i)}}}}\end{matrix}}{\begin{matrix}{{2{N \cdot {\sum\limits_{i = 0}^{{2N} - 1}\; {{{{Rec}_{neig}(i)} \cdot {Rec}_{refneig}}(i)}}}} -} \\\left( {\sum\limits_{i = 0}^{{2N} - 1}\; {{Rec}_{refneig}(i)}} \right)^{2}\end{matrix}}} & {{Equation}\mspace{14mu} (2)}\end{matrix}$

In some cases, only a is used in the linear model and b is always setequal to 0. In some cases, only b is used and a is always set equal to1.

In HEVC, Weighted Prediction (WP) is supported, in which case a scalingfactor (denoted by a), a shift number (denoted by s) and an offset(denoted by b) is used in the motion compensation. Suppose the pixelvalue in position (x, y) of the reference picture is p(x, y), then p′(x,y)=((a*p(x, y)+(1<<(s−1)))>>s)+b instead of p(x, y) is used as theprediction value in motion compensation.

When WP is enabled, for each reference picture of current slice, a flagis signaled to indicate whether WP applies for the reference picture ornot. If WP applies for one reference picture, a set of WP parameters(i.e., a, s and b) is sent to the decoder and is used for motioncompensation from the reference picture. In some examples, to flexiblyturn on/off WP for luma and chroma component, WP flag and WP parametersare separately signaled for luma and chroma component. In WP, one sameset of WP parameters is used for all pixels in one reference picture.

With respect to local illumination compensation (LIC) in JVET, LIC isbased on a linear model for illumination changes, using a scaling factora and an offset b. Such LIC is enabled or disabled adaptively for eachinter-mode coded coding unit (CU). When LIC applies for a CU, a leastsquare error method is employed to derive the parameters a and b byusing the neighboring samples of the current CU and their correspondingreference samples. More specifically, as illustrated in FIG. 5A and FIG.5B, the subsampled (2:1 subsampling) neighboring samples of the CU andthe corresponding pixels (identified by motion information of thecurrent CU or sub-CU) in the reference picture are used. In someexamples, the IC parameters are derived and applied for each predictiondirection separately.

When a CU is coded with merge mode, the LIC flag is copied fromneighboring blocks, in a way similar to motion information copy in mergemode; otherwise, an LIC flag is signalled for the CU to indicate whetherLIC applies or not.

Overlapped block motion compensation (OBMC) was proposed in thedevelopment of H.263. For example, OBMC can be performed on an 8×8block, and motion vectors of two connected neighboring 8×8 blocks areused for current block, as shown in FIG. 6. For example, for the first8×8 block in the current macroblock, besides its own motion vector, theabove and left neighboring motion vector are also applied to generatedtwo additional prediction blocks. In this way, each pixel in the current8×8 block have three prediction values and weighted average of thesethree prediction values is used as the final prediction.

When a neighboring block is not coded or is coded as intra (usingintra-prediction), meaning that the neighboring block does not have anavailable motion vector, the motion vector of current 8×8 block is usedas the neighboring motion vector. Meanwhile, for the third and fourth8×8 blocks of the current macroblock (as shown in FIG. 6), the belowneighboring block is always not used. In other words, for each MB, nomotion information from MBs below it will be used to reconstruct thepixels of the current MB during the OBMC.

In HEVC, OBMC was also proposed to smooth the PU boundary, as describedin U.S. Publication Nos. US2013/0128974 and US2012/0177120, which arehereby incorporated by reference in their entirety for all purposes. Anexample of the proposed method is show in FIG. 7A and FIG. 7B. When a CUcontains two (or more) PUs, lines and/or columns near the PU boundaryare smoothed by OBMC. For a pixel marked with “A” or “B” in PU0 or PU1,two prediction values are generated (e.g., by applying motion vectors ofPU0 and PU1, respectively), and weighted average of them are used as thefinal prediction.

In Joint Exploration Test Model 3.0 (JEM), sub-PU level OBMC is applied.The OBMC is performed for all Motion Compensated (MC) block boundariesexcept the right and bottom boundaries of a CU. Moreover, it is appliedfor both luma and chroma components. In HEVC, a MC block iscorresponding to a PU. In JEM, when a PU is coded with sub-PU mode, eachsub-block of the PU is a MC block. To process CU/PU boundaries in auniform fashion, OBMC is performed at sub-block level for all MC blockboundaries, where sub-block size is set equal to 4×4, as illustrated inFIG. 8A and FIG. 8B.

When OBMC applies to a current sub-block, besides current motionvectors, motion vectors of four connected neighboring sub-blocks, ifthey are available and are not identical to the current motion vector,are also used to derive prediction block for the current sub-block.These multiple prediction blocks based on multiple motion vectors areweighted to generate the final prediction signal of the currentsub-block.

A prediction block based on motion vectors of a neighboring sub-block isdenoted as P_(N), with N indicating an index for the neighboring above,below, left and right sub-blocks and the prediction block based onmotion vectors of the current sub-block is denoted as P_(C). When P_(N)belongs to the same PU as P_(C) (thus contains the same motioninformation), the OBMC is not performed from P_(N). Otherwise, everypixel of P_(N) is added to the same pixel in P_(C), e.g., fourrows/columns of P_(N) are added to P_(C). The weighting factors {¼, ⅛,1/16, 1/32} are used for P_(N) and the weighting factors {¾, ⅞, 15/16,31/32} are used for P_(C). The exception are small MC blocks, (i.e.,when PU size is equal to 8×4, 4×8 or a PU is coded with ATMVP mode), forwhich only two rows/columns of P_(N) are added to P_(C). In this case,weighting factors {¼, ⅛} are used for P_(N) and weighting factors {¾, ⅞}are used for P_(C). For P_(N) generated based on motion vectors ofvertically (horizontally) neighboring sub-block, pixels in the same row(column) of P_(N) are added to P_(C) with a same weighting factor. Notethat for PU boundaries, OBMC can be applied on each side of theboundary. Such as in FIG. 8A and FIG. 8B, OBMC can be applied alongboundary between PU1 and PU2 twice. First, OBMC is applied with PU2's MVto the shaded blocks along the boundary inside PU1. Second, OBMC isapplied with the PU1's MV to the shaded blocks along the boundary insidePU2. In contrast, OBMC can only be applied to one side of CU boundariesbecause when coding the current CU, CUs which have been coded cannot bechanged.

Frame rate up-conversion (FRUC) technology is used to generatehigh-frame-rate videos based on low-frame-rate videos. FRUC has beenwidely used in display industry. FRUC algorithms can be divided into twotypes. One type of FRUC methods interpolate intermediate frames bysimple frame repetition or averaging. However, this method providesimproper results in a picture that contains a lot of motion. The othertype of FRUC methods, called motion-compensated FRUC (MC-FRUC), considerobject movement when it generates intermediate frames and includes twosteps: (1) motion estimation (ME) and (2) motion-compensatedinterpolation (MCI). ME generates motion vectors (MVs), which representobject motion using vectors, whereas MCI uses MVs to generateintermediate frames.

The block-matching algorithm (BMA) is widely used for ME in MC-FRUC, asit is simple to implement. BMA divides an image into blocks and detectsthe movement of those blocks. Two kinds of ME are primarily used forBMA, including: unilateral ME and bilateral ME.

FIG. 9 illustrates unilateral ME in FRUC. As shown in FIG. 9, unilateralME obtains MVs by searching the best matching block from a referenceframe of the current frame. Then the block on the motion trajectory inthe interpolated frame can be located so that the MV is achieved. Asshown in FIG. 9, three blocks in three frames are involved following themotion trajectory. Although the block in the current frame belongs to acoded block, the best matching block in the reference frame may notfully belong to a coded block; in some cases, neither does the block inthe interpolated frame. Consequently, overlapped regions of the blocksand un-filled (holes) regions may occur in the interpolated frame.

To handle overlaps, simple FRUC algorithms merely involve averaging andoverwriting the overlapped pixels. Moreover, holes are covered by thepixel values from a reference or a current frame. However, thesealgorithms result in blocking artifacts and blurring. Hence, motionfield segmentation, successive extrapolation using the discrete Hartleytransform, and image inpainting are proposed to handle holes andoverlaps without increasing blocking artifacts and blurring.

FIG. 10 illustrates bilateral ME in FRUC. As shown in FIG. 10, bilateralME is another solution (in MC-FRUC) that can be used to avoid theproblems caused by overlaps and holes. Bilateral ME obtains MVs passingthrough a block in the intermediate frame using the temporal symmetrybetween blocks of the reference and current frames. As a result, it doesnot generate overlaps and holes. Since it is assumed the current blockis a block that is being processed, in a certain order, e.g., as in thecase of video coding, a sequence of such blocks would cover the wholeintermediate picture without overlap. For example, in the case of videocoding, blocks can be processed in the decoding order. Therefore, insome examples, such a method may be more suitable if FRUC ideas can beconsidered in a video coding framework.

Decoder side motion vector derivation can also be performed. Due toadvanced video codecs, a better bit percentage of motion information inbitstream can be achieved. To reduce the bit cost of motion information,Decoder side Motion Vector Derivation (DMVD) was proposed.

Template matching based DMVD shows good coding efficiency improvement.FIG. 11A and FIG. 11B illustrate the idea of template matching basedDMVD. Instead of searching best match for the prediction target, whichis the current block at the decoder, best match of template is searchedin the reference frame. Assuming the template and the prediction targetare from the same object, the motion vector of the template can be usedas the motion vector of the prediction target. Since the templatematching is conducted at both encoder and decoder, the motion vector canbe derived at decoder side to avoid signaling cost.

Another category of DMVD is mirror based bi-directional MV derivation.The idea is similar to bilateral ME in FRUC. Mirror-based MV derivationis applied by centro-symmetric motion estimation around search centersin fractional sample accuracy. The size and/or location of the searchwindow can be pre-defined and can be signaled in bitstream. FIG. 12illustrates mirror based bi-directional MV derivation in DMVD. The termdMV in FIG. 12 is an offset which is added to PMV0 and is subtractedfrom PMV1 to generate a MV pair, MV0 and MV1. All the values of dMVinside the search window will be checked and the Sum of AbsoluteDifference (SAD) between the L0 and L1 reference blocks is used as themeasurement of Centro-symmetric motion estimation. An MV pair with theminimum SAD is selected as the output of Centro-symmetric motionestimation. Since the method needs a future reference (reference at atemporal position later than the current frame) and an earlier reference(reference at a temporal position earlier than the current frame) forthe SAD matching, it is cannot be applied to P frame or low-delay Bframes in which only former reference is available.

In some cases, it has been proposed to combine the mirror basedbi-directional MV derivation with merge mode in HEVC. For example, aflag called pu_dmvd_flag is added for a PU of B slices to indicate ifDMVD mode is applied to the current PU. FIG. 13 is a flowchart of PUdecoding with pu_dmvd_flag added. Since DMVD mode does not explicitlytransmit any MV information in the bitstream, the decoding process ofintegrating pu_dmvd_flag with the syntax of Merge mode in HEVC codingprocess is presented as shown in FIG. 13.

Various problems exist with one or more of the techniques describedabove. For example, in existing LIC algorithms, during bi-predictivemotion compensation, LIC parameters are derived independently from Ref0and Ref1 without considering their joint influence on the predictor. Forexample, in a bi-prediction case, separate LIC-compensated predictionpatches are determined, and an equal weight (0.5) is used to combine theLIC-compensated prediction patches to generate the final bi-predictor.Furthermore, in the existing LIC algorithm, only a subset of a singlerow and a single column of neighboring pixels are used to derive the LICparameters, which may lead to sub-optimal solutions. Even further, inthe existing LIC algorithm, integer-positioned pixels are used to derivethe LIC parameters without filtering (without fractional-pel accuracy),which may lead to producing sub-optimal parameters due to noisyreconstructed pixels. Also, when LIC is enabled, OBMC is also enabledfor Bi-predictive motion compensation, which may lead to over-smoothingthe boundary pixels of blocks.

Various techniques are described herein to solve the aforementionedproblems. In some cases, the techniques described herein may be appliedindividually. In some cases, any combination of the techniques describedherein may be applied. In this application, in some cases, referenceindex information is regarded as a part of motion information. In someexamples, they are jointly called as a set of motion information.

In some examples, methods and systems are described herein for derivingone or more local illumination compensation (LIC) parameters for a blockof a picture based on templates of multiple reference pictures. Both theencoder and decoder can follow the same procedure to derive theillumination compensation parameters using the techniques describedherein. For example, both the encoder and decoder can derive weights (orscaling factors) and an offset using the same procedure without theparameters having to be signaled (e.g., to the decoder) in the bitstreamor using another signaling mechanism. In some cases, the only differencein the encoder and decoder LIC parameter derivation is that, at theencoder side, it may need to perform a joint optimization between theswitch of LIC and motion search. In some examples, an exhaustive searchcan be employed.

The LIC method described herein includes an alternative method to solvethe LIC parameters for bi-predictive motion compensation. For instance,during bi-predictive motion compensation, the LIC parameters can bederived by considering the template of both a block (Ref0) of a firstreference picture from reference picture list 0 (RefPicList0) and ablock (Ref1) of a second reference picture from reference picture list 1(RefPicList1) simultaneously. In one example, a first template of thefirst reference picture and a second template of the second referencepicture are used simultaneously to derive one or more local illuminationcompensation parameters. Such a technique provides a more optimalpredictor than existing techniques that derive LIC parametersindependently from Ref0 and Ref1 without considering their jointinfluence on the predictor. For example, using existing LIC solutions,the LIC parameters are derived by finding the solution of a pair of datasets formed by the neighboring pixels between current reconstructedframe and a reference frame. In bi-predictive motion compensation, thecalculation of the existing LIC solution is done with respect toreference blocks of L0 and L1 individually, using separate costfunctions. An equal-weight bi-averaging operation has to be used tocombine the LIC-compensated predictors. Deriving the LIC parametersseparately for Ref0 and Ref1 may pose an issue when the temporaldistance of the two reference frames to the current frames are unequal.Also, when there is a non-uniform illumination change temporally, theequal-derivation of the LIC parameter may result in sub-optimalparameters when it comes to bi-prediction.

FIG. 14 is a diagram illustrating template-based derivation of LICparameters. The current block 1402 is a block of the current picture forwhich motion compensation is being performed. The reference pictureblock 1404 is a block (Ref0) of a first reference picture from referencepicture list 0 (RefPicList0), and the reference picture block 1406 is ablock (Ref1) of a second reference picture from reference picture list 1(RefPicList1). The term P0 denotes the template region of Ref0, and theterm P1 denotes the template region of Ref1, respectively. The termN_(i) denotes the template region of the current block 1402. The samplesin the template Ni are part of a reconstructed block of a reconstructedframe neighboring the current block 1402.

Illumination compensation parameters can include an offset, one or moreweights, a shift number, or other suitable illumination compensationparameters. A weight can also be referred to as a scaling factor. Byusing templates of a first reference picture and a second referencepicture, for example, the one or more weights can include a first weightfor the template of the first reference picture and a second weight forthe template of the second reference picture.

In some implementations, a linear least square regression can be used toestimate the LIC parameters in bi-predictive motion compensation. In oneexample, the derivation of the LIC parameters can be done by solving acost function (e.g., Eq. (4) or Eq. (10) below) using the belowleast-square equations (e.g., Eqs. (5)-(6) or Eqs. (5) and (11) below).For instance, a subset of samples from one or more neighboring blocks ofthe current block can be used to derive the LIC parameters. Samples fromneighboring blocks of the current block can be used to find a possibleilluminance changes in the current block 1402, because it can be assumedthat there is a strong correlation between the neighboring samples (inthe neighboring blocks) and the current samples (in the current block1402). For instance, it can be assumed that the current block and theneighboring block, which share the same motion information, shouldcontain very similar illuminance values. Another reason to useneighboring samples is that the current block has not yet beenpredicted, and there may not be pixels to use from the current block, inwhich case the neighboring samples (which have been reconstructed) canbe used in performing the template matching for motion compensation ofthe current block.

In one illustrative example, either a top neighbor, a left neighbor, orboth top neighbor and the left neighbor may be used. For instance, thetemplate N_(i) shown in FIG. 14 can include a subset of samples from atop neighbor and a left neighbor of the current block 1402. The templateP0 shown in FIG. 14 can include a subset of pixels from a top neighborand a left neighbor of the reference block 1404, and the template P1 caninclude a subset of pixels from a top neighbor and a left neighbor ofthe reference block 1406. The samples of the neighboring blocks used inthe templates P0 and P1 can include samples corresponding to theneighboring samples used in the template N_(i). In some cases, thecorresponding samples used in templates P0 and P1 can be identified bymotion information of the current block. In one illustrative example atthe decoder side, the motion vectors can be signaled in the bitstream,through either the merge mode, FRUC merge mode, or the regular AMVPmode. The decoder can reconstruct the motion information (e.g., motionvectors and reference indexes) and the reference picture order count(POC). The decoder can identify the reference pictures using thereference indexes, and can identify the reference blocks 1404 and 1406within the reference pictures using the motion vectors. The decoder canthen derive the associated template regions P0 and P1 of the referenceblocks 1404 and 1406. For example, once the reference blocks 1404 and1406 are determined in the reference pictures, the top and leftneighboring samples (e.g., one or more rows and one or more columns)from neighboring blocks can be determined as the template regions P0 andP1. Such a technique is different from FRUC template matching, where thetemplate of the current block is first determined, then the template isused to search the motion vectors on given reference frames.

In some examples, to solve the weights for bi-predictive LIC, thefollowing cost function is considered:

$\begin{matrix}{E = {{\frac{1}{2}{\sum\limits_{i = 0}^{N - 1}\; \left( {N_{i} - {w_{0}P_{0,i}} - {w_{1}P_{1,i}} - o} \right)^{2}}} + {\frac{\lambda}{2}\left( {w_{0} + w_{1} - 1} \right)^{2}}}} & {{Equation}\mspace{14mu} (4)}\end{matrix}$

where λ is a regularization parameter, the term N_(i) is the topneighboring pixels and/or the left neighboring pixels of the currentblock in the current reconstructed frame (e.g., the template N_(i) ofthe current block 1402 shown in FIG. 14), the terms P_(0,i) and P_(1,i)are the top and/or the left neighboring pixels of the referenced blockin the reference frames of List0 and List1 (e.g., the template P0 ofreference block 1404 and the template P1 of reference block 1406 shownin FIG. 14), respectively, the term i is the pixel index within thetemplate region, and the term N is the total number of pixels in thetemplate region (N_(i), P0, and/or P1).

The term o is the offset, and the terms w⁰ and w₁ are the weights. Theweights w₀ and w₁ and the offset o are used to compensate for thediscrepancy induced by illumination changes in a series of picture. Forexample, the offset o can indicate the average luminance change byconsidering the two reference frames simultaneously. The weight w₀ ismultiplied by the prediction samples generated from the reference block1404 (from List0), which are the samples in the template P0 shown inFIG. 14. The weight w₁ is multiplied by the prediction samples generatedfrom the reference block 1406 (from List1), which are the samples in thetemplate P1 shown in FIG. 14. The weights w₀ and w₁ are adjustableparameters and are based on certain characteristics of a picture. Forexample, the weights w₀ and w₁ can be based on the temporal distance ofthe reference picture being used to predict the current picture, basedon whether the picture is becoming lighter or darker, or othercharacteristics. In one example, if there are two reference pictures,with the first reference picture sitting closer to the current picturethan the second reference picture, different weights can be applied tothese two different reference pictures to find better predictionexamples for the current block for which motion compensation is beingperformed. For instance, a smaller weight can be applied to samples ofthe second reference picture (which is further away from the currentpicture) than a weight that is applied to samples of the first referencepicture (which is closer to the current picture). In another example, ahigher weight can be applied to samples that have less illuminationchange. For example, as shown by eqs. (6) below, a cross correlation istaken from neighboring samples to the prediction samples of a firstreference frame, and, if the reference frame is farther away andneighboring samples of the first reference frame are darker than theneighboring samples of a second reference frame, then the weight can bemade less. The final prediction is generated according to Eq. (9).

Eq. (4) can be solved using ordinary linear least-square regression toobtain the values of the weights w₀ and w₁ and the offset o. Forexample, by solving Eq. (4) using linear least-square regression, thesolution to eq. (4) can be found as:

$\begin{matrix}{{w_{0} = \frac{{c \cdot d} - {b \cdot e}}{{a \cdot c} - b^{2}}}{w_{1} = \frac{{a \cdot e} - {b \cdot d}}{{a \cdot c} - b^{2}}}{o = \frac{\left( {{\sum\limits_{i = 0}^{N - 1}\; N_{i}} - {w_{0}{\sum\limits_{i = 0}^{N - 1}\; P_{0,i}}} - {w_{1}{\sum\limits_{i = 0}^{N - 1}\; P_{1,i}}}} \right)}{N}}} & {{Equations}\mspace{14mu} (5)}\end{matrix}$

Accordingly, the weights and offset can be found by solving Eq. (4). Insome cases, if the determinant of the least square solution (term a·c−b²in Eqs. (5)) is equal to zero, the unidirectional LIC can be used (usinga single reference block at a time) instead of bi-directional LIC (usingtwo reference blocks simultaneously). In some cases, to avoidover-compensation, the offset o in Eqs. (5) can be further constrained.One example of the values can be associated with the bit depth (BD),where the offset can be restricted to the range of [−2^(BD), 2^(BD)−1].

In Eqs. (5), N is the number of pixels in the template being analyzed(N_(i), P0, and/or P1), and the terms {a, b, c, d, e} are defined asfollows:

$\begin{matrix}{{{a = {{\sum\limits_{i = 0}^{N - 1}\; P_{0.i}^{2}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} \right)^{2}}{N} + \lambda}}b = {{\sum\limits_{i = 0}^{N - 1}\; {P_{0,i}P_{i,1}}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} \right)\left( {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} \right)}{N} + \lambda}}{c = {{\sum\limits_{i = 0}^{N - 1}\; P_{1.i}^{2}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} \right)^{2}}{N} + \lambda}}{d = {{\sum\limits_{i = 0}^{N - 1}\; {P_{0,i}N_{i}}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} \right)\left( {\sum\limits_{i = 0}^{N - 1}\; N_{i}} \right)}{N} + \lambda}}{e = {{\sum\limits_{i = 0}^{N - 1}\; {P_{1,i}N_{i}}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} \right)\left( {\sum\limits_{i = 0}^{N - 1}\; N_{i}} \right)}{N} + \lambda}}} & {{Equation}\mspace{14mu} (6)}\end{matrix}$

The terms a and c represent the variance across the samples from thetemplate P0 and the template P1, respectively. For example, the term arepresents a variance of the prediction samples of the template P0 forthe reference block 1404 (Ref0), and the term c represents a variance ofthe prediction samples of the template P1 for the reference block 1406(Ref1). Using a as an example, a sample value P_(0,i) from the templateP0 is squared, and the mean of the samples in the template P0 issubtracted from the squared sample value P_(0,I), which provides thevariance of the sample value P_(0,i). The mean is shown as the sum ofall the samples in the template P0, squared, divided by the total numberof samples in the template P0. The regularization parameter λ is alsoused (for each of the terms a-e), as described below. The definition ofthe term c is similar to the definition of the term a, but with respectto a sample value P_(1,i) from the template P1.

The term b is related to the covariance (or cross correlation in somecases) of the corresponding samples in P0 and P1. The term d is relatedto the covariance (or cross correlation in some cases) between thesamples in the template P0 and the corresponding samples in the templateN_(i). Similarly, term e is related to the cross correlation between thesamples in the template P1 and the corresponding samples in the templateN_(i). As shown in eqs. (5), the weights w₀ and w₁ are determined basedon the terms a, b, c, d, and e. The weights w₀ and w₁ represent ameasure of similarity between the current neighboring samples (of thecurrent block) and the referenced neighbors of the reference blocks. Ifthe variance of the other referenced neighbors is high, or thecovariance between the referenced neighbors and the current neighbors ishigh, the weights are higher. If the covariance of the two referencedneighbors is high, or the covariance of the current neighbors and thereferenced neighbors is high, the weighting factor is lower.

The equations (6) can re-written as:

a=N·VAR(P ₀)+λ

b=N·COV(P ₀ ,P ₁)+λ

c=N·VAR(P ₁)+λ

d=N·COV(N _(i) ,P ₀)+λ

e=N·COV(N _(i) ,P ₁)+λ  Equations (6)′

The value of the regularization parameter λ can be chosen as a positivevalue:

$\begin{matrix}{\lambda = {k \cdot \left( {{\sum\limits_{i = 0}^{N - 1}\; P_{0,i}^{2}} + {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}^{2}}} \right)}} & {{Equation}\mspace{14mu} (7)}\end{matrix}$

where k is a scaling factor whose absolute value is less than one.Alternatively, λ can be chosen to be the maximum of the two sum ofsquares:

$\begin{matrix}{\lambda = {k \cdot {\max \left( {{\sum\limits_{i = 0}^{N - 1}\; P_{0,i}^{2}},{\sum\limits_{i = 0}^{N - 1}\; P_{1,i}^{2}}} \right)}}} & {{Equation}\mspace{14mu} (8)}\end{matrix}$

The final prediction samples are created by:

P(x,y)=w ₀ P ₀(x,y)+w ₁ P ₁(x,y)+o  Equation (9)

-   -   where (x, y)εPU_(c)

The final prediction sample P(x,y) represents a sample value that willbe used for a sample at a position (x,y) in the current block 1402. Asdescribed herein, the application of the LIC can be integrated into theconventional bi-predictive motion compensation. When considering thetemplate-based search to find the optimal weight, Eq. (9) can still beused to apply the optimal weights during bi-predictive motioncompensation.

In some examples, more than one derivation method to derive the LICparameters can be performed. In such examples, the encoder or othertransmitter-side device can signal to the decoder which derivationmethod is to be used at a sequence level (e.g., in the VPS and/or theSPS), at the picture level (e.g., in the PPS), at the slice level (e.g.,in the slice header), at the CTU level, at CU level, at PU level, or acombination thereof, or other suitable signaling level.

Another illustrative example of an alternative cost function that beused is defined as:

$\begin{matrix}{E = {{\frac{1}{2}{\sum\limits_{i = 0}^{N - 1}\; \left( {N_{i} - {w_{0}P_{0,i}} - {w_{1}P_{1,i}} - o} \right)^{2}}} + {\frac{\lambda}{2}\left( {w_{0} - 0.5} \right)^{2}} + {\frac{\lambda}{2}\left( {w_{1} - 0.5} \right)^{2}}}} & {{Eq}.\mspace{14mu} (10)}\end{matrix}$

The linear least square solution to the cost function in Eq. (10) has asimilar form of Eq. (5), but with different definitions for each term in{a, b, c, d, e}:

$\begin{matrix}{{{a = {{\sum\limits_{i = 0}^{N - 1}\; P_{0.i}^{2}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} \right)^{2}}{N} + \lambda}}b = {{\sum\limits_{i = 0}^{N - 1}\; {P_{0,i}P_{i,1}}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} \right)\left( {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} \right)}{N}}}{c = {{\sum\limits_{i = 0}^{N - 1}\; P_{1.i}^{2}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} \right)^{2}}{N} + \lambda}}{d = {{\sum\limits_{i = 0}^{N - 1}\; {P_{0,i}N_{i}}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} \right)\left( {\sum\limits_{i = 0}^{N - 1}\; N_{i}} \right)}{N} + {0.5 \cdot \lambda}}}{e = {{\sum\limits_{i = 0}^{N - 1}\; {P_{1,i}N_{i}}} - \frac{\left( {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} \right)\left( {\sum\limits_{i = 0}^{N - 1}\; N_{i}} \right)}{N} + {0.5 \cdot \lambda}}}} & {{Equation}\mspace{14mu} (11)}\end{matrix}$

More generally, Eq. (10) can be defined as:

$\begin{matrix}{E = {{\frac{1}{2}{\sum\limits_{i = 0}^{N - 1}\; \left( {N_{i} - {w_{0}P_{0,i}} - {w_{1}P_{1,i}} - o} \right)^{2}}} + {\frac{\lambda}{2}\left( {w_{0} - {Default}_{W\; 0}} \right)^{2}} + {\frac{\lambda}{2}\left( {w_{1} - {Default}_{W\; 1}} \right)^{2}}}} & {{Equation}\mspace{14mu} (12)}\end{matrix}$

The value of Default_(W0) and Default_(W1) can be set to any suitablevalue, and can be signaled in the bitstream at different levels, such asat the picture level, the slice level, the block level, or at the levelof a group of blocks. As one example, the weighted prediction parametersignaled in the slice header can be used to derive the value ofDefault_(W0) and Default_(W1). The example cost function in eq. (10)uses a value of 0.5 for both of the Default_(W0) and Default_(W1) terms.However, such terms are configurable and can be set to any suitablevalue.

In some examples, the least square solution can be calculated based onmultiple lines and/or columns of template from a neighbor (e.g., eithertop neighbor, a left neighbor, both the top and left neighbors, or otherneighbors). Example numbers (and in some cases, the typical numbers) oflines and/or columns includes one, two, four, or any other suitablenumber of rows and/or columns. For instance, more than one line and/orcolumn of samples from the left neighbor of the current block 1402, andmore than one line and/or column of samples from the top neighbor of thecurrent block 1402 can be included in the template N_(i). In such cases,there will be a corresponding number of lines and/or columns of samplesin the templates P0 and P1. In one illustrative example, the templateN_(i) can include 2 columns of pixels from the left neighboring block ofthe current block 1402, and 2 rows of pixels from the top neighboringblock of the current block 1402. In such an example, the template P0 caninclude 2 columns of pixels from the left neighboring block of thereference block 1404, and 2 rows of pixels from the top neighboringblock of the reference block 1404. Similarly, in such an example, thetemplate P1 can include 2 columns of pixels from the left neighboringblock of the reference block 1406, and 2 rows of pixels from the topneighboring block of the reference block 1406.

The equations 4-11 above may be modified when multiple lines and/orcolumns are included in a template. For example, the number of pixels inthe template region (the term N) would change, based on the number oflines and/or columns in the template. For example, if the blocks are16×16 blocks (16 rows of pixels by 16 columns of pixels), and if twolines from the top neighboring block and two columns from the leftneighboring block are used, the N_(i) template will include 64 samples(32 samples from the left neighboring block and 32 samples from the topneighboring block), and the value of N will be 64. In such an example,the P0 and P1 templates will also include 64 samples.

In some cases, integer-positioned samples (or pixels) are used for thederivation of the LIC parameters. In some cases, fractional-positionedsamples are used for the derivation of the LIC parameters. In somecases, integer-positioned samples and fractional-positioned samples canboth be used. For example, the true displacements of moving objectsbetween pictures are continuous and tend to not follow the sampling gridof the pictures in a video sequence. Because of this, fractionalaccuracy can be used for motion vectors instead of integer accuracy,leading to a decrease in residual error and an increase in codingefficiency of video coders. If a motion vector has a fractional value,the reference block needs to be interpolated accordingly. For example, amotion vector for a sample of a current block can point to afractional-pel position in a reference block. A fractional-pel positionrefers to samples (e.g., a luma sample) at fractional sample locations(non-integer locations) in the block. Such locations need to begenerated by interpolation. In one example when factional-positionedsamples are used, an interpolated or filtered version of the template(e.g., P0 or P1) can be used to reduce the quantization error from thereconstructed pixels when deriving the LIC parameters. Such aninterpolated version of a template can be generated using one or moreinterpolation filters. For example, if a motion vectors of a currentblock points to a fractional-pel position in a reference frame, aninterpolation filter can be used to generate a better set of samples forthe template before deriving the LIC parameters. For example, the typeof interpolation filters used can include, but are not limited to, abi-linear interpolation filter, an 8-tap interpolation filter, definedin the HEVC standard, or any other suitable filter. Currentlyillumination compensation solutions do not use any fractional-pelpositioned samples. For instance, using current solutions, assuming amotion vector points to a fractional-pel position, the value of thepredictor to be used in LIC derivation is rounded to the nearest integerreference sample position, and then the resulting samples are used toderived the LIC parameters.

In one example, some samples from the templates (P0 and P1) can bedetermined to be outliers and can be excluded. For example, the leastsquare solution can be calculated based on samples excluding outliers.In some implementations, decoded or derived sample value range(s) (orthresholds) can be applied to remove outliers. The range can be referredto as an outlier threshold range. Samples whose values are not withinthe range can be removed, and the least square solution is calculatedbased on the samples whose values are within the range. In oneillustrative example, 8-bit pixel values can be used, in which case apixel value can be from 0-255. In some cases, the values of pixels in agiven picture can include a subset of all the available values, such asa subset of pixel values between 16-235. The subset of values used in agiven picture can be used as the range for excluding outliers. Anysample value that is outside of the range can be determined to be anoutlier, and can be removed from the template before deriving the LICparameters using the equations above. In another illustrative example, amean value of the sample values in the template can be computed, and therange can include x-standard deviations from the mean. The x term can beset to any suitable value, such as 3 (for 3 standard deviations), 4, 5,or other suitable value. Any sample beyond the x-standard deviationsfrom the mean can be excluded. The range can be signaled to decoder,such as at the slice level, picture level, block level, or the like.

In some examples, only the luma component needs to be used to jointlyoptimize the LIC parameters for both Ref0 and Ref1. Alternatively, bothluma and chroma components can be considered during the derivation ofthe bi-predictive LIC parameters. The encoder can signal to the decoder(in a parameter set, in an SEI message, or other suitable signalingmechanism) whether or not to apply LIC to one or more of the chromacomponents, or only to apply LIC to the luma components.

In some cases, when FRUC bilateral matching is enabled, thebi-predictive LIC derivation can be skipped and the system can proceedwith uni-directional LIC. In some cases, FRUC and bi-lateral (templatebased) LIC can be used together.

In some examples, the Overlapped Block Motion Compensation (OBMC)technique previously described can be used disjoint when LIC (e.g.,either bi-predictive and/or uni-predictive LIC) is enabled. For example,in some cases, when LIC is enabled for a block, OBMC is disabled for theblock. In another example, when LIC is enabled, OBMC is disabled forB-type slices only. In such examples, the OBMC flag and the IC flag(e.g., in the syntax of a parameter set, in a header, in an SEI message,or the like) can be enabled together only for the blocks in P-typeslice. In another example, when LIC is enabled, OBMC is disabled onlyfor bi-predicted blocks. In such examples, the OBMC and IC techniquescan simultaneously be applied only for uni-predicted blocks.

Additionally, if a flag is used (e.g., in the syntax of a parameter set,in a header, in an SEI message, or the like) to indicate whether OBMC isapplied or not, the associated OBMC flag should not be sent when OBMCand LIC cannot be enabled together for a block, a slice, a picture, orthe like. Similarly, the constraint can be applied to the LIC flag incase of an OBMC flag being firstly signaled.

FIG. 15 illustrates a process 1500 for the existing signaling betweenthe IC and the OBMC flags (blocks 1504 and 1506), as well as the flowcharts on the improved signaling (blocks 1502 and 1508-1518). It isproposed that using example 1, example 2, or example 3 above can achievelower encoding complexity and better coding efficiency than existingtechniques. For example, at block 1502, the process 1500 signals themotion vector and reference index for a current block. Using existingtechniques, the OBMC flag (at block 1504) and the IC flag (at block15060 are signaled. However, in example 1, the process 1500 checkswhether the IC flag is signaled at block 1508. If the IC flag issignaled, the OBMC flag is not signaled. However, if the IC flag is notsignaled, the OBMC flag is signaled at block 1510. When the OBMC flag isnot signaled, it is assumed to be disabled for the current block.

In example 2, the process 1500, at block 1512, checks both whether theIC flag is signaled and whether the current slice is a B-type slice. Ifthe IC flag is signaled and the current slice is a B-type slice, theOBMC flag is not signaled. However, if the IC flag is not signaled orthe current slice is a B-type slice, the OBMC flag is signaled at block1514. When the OBMC flag is not signaled, it is assumed to be disabledfor the current block.

In example 3, the process 1500, at block 1516, checks both whether theIC flag is signaled and whether the current block is a bi-predictedblock. If the IC flag is signaled and the current block is abi-predicted block, the OBMC flag is not signaled. However, if the ICflag is not signaled or the current block is a bi-predicted block, theOBMC flag is signaled at block 1518. When the OBMC flag is not signaled,it is assumed to be disabled for the current block.

One or more of the above-described examples provide an alternativemethod to the existing Local Illumination Compensation (LIC) tool in JEM3.0. In some of the examples, a linear least-square method is used tosolve the LIC parameters for both L0 and L1 jointly in bi-predictivemotion compensation. Tested on JEM-3.0 under the common test condition,the proposed method may provide 0.18%/0.01%/xxx % BD-rate reduction forrandom access, low-delay B, and low-delay P configurations,respectively, with 2-3% encoding time increase.

Experiments have shown positive results using the template-basedbi-predictive LIC derivation techniques described herein. In thefollowing simulation, the value of lambda is chosen to be:

$\begin{matrix}{\left( {{\sum\limits_{i = 0}^{N - 1}\; P_{0,i}} + {\sum\limits_{i = 0}^{N - 1}\; P_{1,i}} + 64} \right)7} & {{Equation}\mspace{14mu} (12)}\end{matrix}$

TABLE 1 Random Access Main 10 Over JEM-3.0 Y U V EncT DecT Class A1−0.27% 0.63% −0.36% 101% 102% Class A2 −0.10% −0.06% −0.14% 102% 101%Class B −0.13% 0.12% 0.21% 102% 101% Class C −0.20% −0.04% 0.02% 102%102% Class D −0.19% −0.26% −0.23% 102% 101% Class E Overall (Ref) −0.18%0.08% −0.09% 102% 101% Class F −0.73% −0.27% −0.16% 98% 99% (optional)

TABLE 2 Low delay B Main10 Over JEM-3.0 Y U V EncT DecT Class A1 ClassA2 Class B 0.05% −0.01% 0.19% 102% 103% Class C −0.02% −0.46% −0.75%103% 102% Class D −0.11% −0.29% −0.88% 103% 103% Class E 0.06% −0.24%0.08% 100% 99% Overall (Ref) −0.01% −0.24% −0.33% 102% 102% Class F−1.04% −0.78% −0.89% 97% 101% (optional)

TABLE 3 Low delay P Main10 Over JEM-3.0 Y U V EncT DecT Class A1 ClassA2 Class B #VALUE! #VALUE! #VALUE! #NUM! #NUM! Class C −0.18% −0.18%−0.02%  105% 114% Class D −0.07% −0.20% 0.20% 104% 107% Class E −0.04%−0.14% 0.37%  97%  97% Overall (Ref) #VALUE! #VALUE! #VALUE! #NUM! #NUM!Class F −0.14% −0.15% 0.00% 104% 106% (optional)

The numbers in the first three columns of Tables 1, 2, and 3 areso-called BD-rate, which is a commonly used metric in video coding tomeasure coding efficiency. Negative numbers for the BD-rate refer to thereduction of bits to represent the video of the same quality and, hence,imply coding gain. The next two columns are the encoding runtime (EncT)and decoding runtime (DecT), respectively. Each of the rows in Tables1-3 indicates a set of sequences of different resolutions from UHD(Class A1/Class A2), HD (Class B), WVGA (Class C), and WQVGA (Class D).Class F is a special set which includes the computer screen contents(SCC).

In some examples, during uni-predictive motion compensation and/orbi-predictive motion compensation, the LIC parameters can be derived bycombining all or any subset of various techniques. In one illustrativeexample, the template can be created by considering all of the samples(e.g., pixels, all luminance samples, all chrominance samples, only oneof the chrominance samples, a combination thereof, or other suitablesample) from the top neighbor, left neighbor, both the top neighbor andthe left neighbor, or another neighboring block.

In some cases, the number of rows and/or columns of pixels (or othersamples) to be included in the regression calculation (e.g., for eitheruni-predictive motion compensation or for bi-predictive motioncompensation) can be one, two, or four. Other suitable numbers of rowsand/or columns can also be used. In some cases, the number of possiblerows and/or columns can be fixed.

In some cases, systems and methods are described herein for adaptivelydetermining the size of one or more templates to use for LIC. Forexample, the number of rows and/or column of samples (e.g., pixels orother samples) in a template (e.g., N_(i), P0, or P1 described above, ora template of a single reference picture used in uni-predictive motioncompensation) used to perform LIC for a current block can vary dependingon a parameter of the current block. The parameter can include the blocksize of the current block (e.g., the width, the height, or the width andheight of the block), a chroma format of the current block (e.g., 4:2:0format, 4:2:2 format, 4:4:4 format, or other suitable chroma format), orother parameter that can be used to determine the template size.

For example, the number of rows and/or columns of pixels (or othersamples) in a template can vary depending on the width and/or height ofthe current block. In some examples, when the block width is less than athreshold width, the number of rows of the top template is one. In someexamples, when the block height is less than a threshold height, thenumber of columns of the left template is one. When the block width ismore than the threshold width, the number of rows of the top template ismore than one, and when the block height is greater than a thresholdheight, the number of columns of the left template is more than one. Inone illustrative example, for block with a width and/or height of lessthan 8 pixels, the number of lines and/or columns is limited to one.Otherwise, if the width and/or height is less than 32 pixels, the numberof lines and/or columns is limited to two. Otherwise, the number oflines and/or columns can be up to 4. In some cases, the thresholds canbe statically decided by the encoder and/or decoder. In some cases, thethresholds or be signaled in the Sequence Parameter Set (SPS), in thePicture Parameter Set (PPS), in the slice header, in an SEI message, orusing other suitable signaling.

In another example, the number of rows and/or columns of pixels (orother samples) for chroma is dependent on a chroma format. For example,for a 4:2:0 format, the number of rows and/or columns of pixels forchroma is set to half of the luma size. In another example, for 4:2:2format, the number of columns of pixels for chroma is set to half of theluma size while the number of rows is set to the same of the luma size.When the number of rows and/or columns of the associated luma componentis one, then the associated number of rows and/or columns can be set toone.

In some examples, the size of the template can be signaled in the SPS,in the PPS, in the slice header, in an SEI message, or using othersuitable signaling. In some examples, the type of interpolation filtersto pre-process the neighboring pixels prior to the regressioncalculation include bi-linear and the 8-tap interpolation filter definedin the HEVC standard, as described herein. In some cases, to type ofinterpolation filters can be signaled via the SPS, the PPS, the sliceheader, an SEI message, or using other suitable signaling.

In some examples, one or more systems and methods are also provided foradaptive selection of weights from a pre-defined set of weights. Forexample, a template-based solution can be used to search for one moreoptimal weights out of the pre-defined set of weights without having tosignal the choice of weights to the decoder. The adaptive weightselection can be used for any template matching based motion predictionor compensation, such as LIC, weighted prediction (WP), or otherprediction or compensation techniques that utilize weights in theprediction process.

For example, if a pre-defined set of weights are considered during thebi-predictive motion compensation, a template-based method can beutilized to search for the optimal set of weights without having tosignal the choice of weights to the decoder. Note that this method canbe applied to both LIC-enabled and LIC-disabled cases, and hence can beapplied independently from some or all of the other methods describedherein. Such methods and the examples below can be applied tobi-predicted blocks and/or uni-predicted blocks.

In some cases, the neighboring samples of the current block can be usedas the template, similarly as that previously described. In some cases,one or more metrics associated with samples for a candidate template canbe used to determine which weights from the pre-defined set of weightsto select. For instance, the sum of absolute differences (SAD), the sumof absolute transformed differences (SATD), and/or the sum of squarederrors (SSE) of the neighboring samples of the current block and theircorresponding samples of one or more reference blocks (indicated by themotion information of the current block) can be used as criteria oftemplate matching. In such an example, the weights from the pre-definedset of weights that result in the smallest SAD, SATD, or SSE of templatematching can be selected and used to generate the prediction. One ofordinary skill will appreciate that any other measurement can be used ascriteria of template matching. In such cases, signaling of one or morespecific weighting parameters is not needed.

In some examples, the metrics (e.g., SAD, SATD, SSE, or the like) oftemplate matching in the pre-defined set can be used for the signalingof the weighting parameter. For example, the order of the SAD/SATD/SSEsof template matching can be used to switch the signaling order of theweighting parameters. In one illustrative example, there are four pairsof weights and the encoder needs to signal which pair of weights to beused. The pair resulting in the lowest SAD/SATD/SSE value is assignedthe codeword of “0”, and the pair resulting in the second lowestSAD/SATD/SSE value is assigned the codeword of “10”. The remaining twopairs are assigned the codeword of “110” and “111”, respectively.

FIG. 16 is a flowchart illustrating an example of a process 1600 ofprocessing video data using one or more of the bi-predictive LICparameter derivation techniques described herein. At 1602, the process1600 includes obtaining the video data. In some examples, the video datacan include encoded video data (e.g., an encoded video bitstream), suchas when the process 1800 is performed by a decoding device. In someexamples, the video data can include un-encoded video data, such as whenthe process 1800 is performed by an encoding device. The video data caninclude a plurality of pictures, and the pictures can be divided into aplurality of blocks, as previously described. The video data can alsoinclude motion information for the pictures and/or blocks, which can beused to perform motion compensation.

At 1604, the process 1600 includes performing bi-predictive motioncompensation for a current block of a picture of the video data.Performing the bi-predictive motion compensation includes deriving oneor more local illumination compensation parameters for the current blockusing a template of the current block, a first template of a firstreference picture, and a second template of a second reference picture.In one illustrative example, the current block can be the current block1402 shown in FIG. 14, the template of the current block can include thetemplate N_(I), the first reference picture can include the referenceblock 1404, the first template can include the template P0, the secondreference picture can include the reference block 1406, and the secondtemplate can include the template P1.

In some examples, the first template of the first reference picture andthe second template of the second reference picture are usedsimultaneously to derive the one or more local illumination compensationparameters. For example, the cost function shown in equation (4) or thecost function shown in equation (10) (or other suitable function) can besolved to derive the one or more local illumination compensationparameters using bo the first reference picture and the second referencepicture at the same time (both reference pictures are used in the samecost function).

In some cases, the template of the current block includes one or morespatially neighboring samples of the current block. For instance, usingFIG. 14 as an example, the template N_(i) is made up of samples from ablock that is neighboring the current block 1402. In such cases, thefirst template includes one or more spatially neighboring samples of thefirst reference block, and the second template includes one or morespatially neighboring samples of the second reference block. Forinstance, again using FIG. 14 as an example, the template P0 includesspatially neighboring samples of the reference block 1404, and thetemplate P1 includes spatially neighboring samples of the referenceblock 1406.

In some examples, the one or more local illumination compensationparameters for the current block can be derived by obtaining the one ormore spatially neighboring samples of the template of the current block.The process 1600 can determine one or more samples of the first templateof the first reference picture. The one or more samples of the firsttemplate include one or more spatially neighboring samples of a firstreference block of the first reference picture. The process 1600 canalso determine one or more samples of the second template of the secondreference picture, which include one or more spatially neighboringsamples of a second reference block of the second reference picture. Forexample, motion information (e.g., motion vectors and two referenceindexes) of the current block can be used to locate first and secondreference pictures (using the reference indexes) and the first andsecond blocks within the reference pictures (using the motion vectors).The one or more spatially neighboring samples of the first and secondreference blocks can then be determined. In one illustrative example,the one or more spatially neighboring samples of the first referenceblock contained in the first template can be determined as the one ormore rows of samples from the neighboring block above the firstreference block and the one or more columns of samples from theneighboring block to the left of the first reference block. In such anexample, the one or more spatially neighboring samples of the secondreference block contained in the second template can be determined asthe one or more rows of samples from the neighboring block above thesecond reference block and the one or more columns of samples from theneighboring block to the left of the second reference block. Rows and/orcolumns from other neighboring blocks can also be used.

The one or more illumination compensation parameters can be derived forthe current block based on the one or more spatially neighboring samplesof the current block, the one or more samples of the first template, andthe one or more samples of the second template. For example, the one ormore local illumination compensation parameters can be derived bysolving a cost function using the offset, the first weight, and thesecond weight. In one illustrative example, the cost function shown inequation (4) or the cost function shown in equation (10) (or othersuitable function) can be solved using the one or more spatiallyneighboring samples of the current block, the one or more samples of thefirst template, and the one or more samples of the second template toderive the one or more local illumination compensation parameters forthe current block. In such an example, the inputs to the LIC procedureinclude the neighboring samples of the current block, the neighboringsamples of the two reference blocks, as well as the two motion vectorsand reference indexes, which indicates where the reference samples comefrom.

In some cases, the template of the current block includes a subset of aplurality of samples of at least one neighboring block of the currentblock. For instance, the template of the current block can include asingle line of pixels from a neighboring block, or multiple lines ofpixels from a neighboring block. In one example, the neighboring samplesmaking up the template can be from a top neighboring block, a leftneighboring block, both the top neighboring block and the leftneighboring block, or other neighboring block. In an example in whichthe template of the current block includes a top neighboring block and aleft neighboring block of the current block, the template can include asingle row from the top neighboring block and a single column of theleft neighboring block. In some examples, the template of the currentblock includes multiple lines of samples from a neighboring block of thecurrent block. In some cases, the template of the current block includesmultiple lines of samples from a first neighboring block and multiplelines of samples from a second neighboring block of the current block.In some cases, the template can include neighboring samples from morethan two neighboring blocks. In an example in which the template of thecurrent block includes a top neighboring block and a left neighboringblock of the current block, the template can include two or more rowsfrom the top neighboring block and two or more columns of the leftneighboring block. The first template of the first reference block andthe second template of the second reference block can also include asingle row and/or column of neighboring blocks of the respectivereference blocks, or multiple rows and/or columns from the neighboringblocks.

In some examples, the one or more local illumination compensationparameters include one or more weights. For instance, the one or moreweights can include a first weight corresponding to the first referencepicture and a second weight corresponding to the second referencepicture. Using the previous examples, the first weight can include theweight w₀ and the second weight can include the weight w₁ from equation(4) or equation (10). In some examples, the one or more localillumination compensation parameters include an offset. Using theexamples from above, the offset can include the offset o from equation(4) or equation (10). In some cases, the one or more local illuminationcompensation parameters include an offset, a first weight correspondingto the first reference picture, and a second weight corresponding to thesecond reference picture.

In some implementations, integer-positioned samples in the firsttemplate of the first reference picture and integer-positioned samplesin the second template of the second reference picture are used forderiving the one or more local illumination compensation parameters. Insome cases, fractional-positioned samples in the first template of thefirst reference picture and fractional-positioned samples in the secondtemplate of the second reference picture are used for deriving the oneor more local illumination compensation parameters. In such cases, theprocess 1600 can use at least one interpolation filter to derive thefractional-positioned samples in the first template of the firstreference picture and the fractional-positioned samples in the secondtemplate.

In some examples, certain samples from the neighboring samples of thefirst and second reference blocks can be excluded from use in derivingthe one or more illumination compensation parameters. For instance, theprocess 1600 can include determining at least one sample from at leastone or more of the first template or the second template that areoutside of an outlier threshold range, and excluding the at least onesample from being used to derive the one or more local illuminationcompensation parameters. For example, as described previously, theoutlier threshold range can include a subset of all the available pixelvalues in the template, an x-standard deviations from the mean of pixelvalues in the template, or other suitable range.

In some cases, only luma components from one or more samples of thefirst template and the second template are used to derive the one ormore local illumination compensation parameters. In some cases, lumacomponents and at least one chroma component from one or more samples ofthe first template and the second template are used to derive the one ormore local illumination compensation parameters.

When performed by a decoder, the process 1600 can further includedecoding the current block using the one or more illuminationcompensation parameters. When performed by an encoder or othertransmitter-side device, the process 1600 can include signaling the oneor more illumination compensation parameters in an encoded videobitstream.

In some examples, Overlapped Block Motion Compensation (OBMC) can bedisabled for the current block when local illumination compensation isenabled for the current block. In some cases, OBMC is disabled forB-type slices of the video data when local illumination compensation isenabled for the video data. In some cases, OBMC is disabled forbi-predicted blocks of the video data when local illuminationcompensation is enabled for the video data.

FIG. 17 is a flowchart illustrating an example of a process 1700 ofprocessing video data using one or more of the adaptive templatederivation techniques described herein. At 1702, the process 1700includes obtaining a current block of a picture of the video data. Insome examples, the video data can include encoded video data (e.g., anencoded video bitstream), such as when the process 1800 is performed bya decoding device. In some examples, the video data can includeun-encoded video data, such as when the process 1800 is performed by anencoding device. The video data can include a plurality of pictures, andthe pictures can be divided into a plurality of blocks, as previouslydescribed. The video data can also include motion information for thepictures and/or blocks, which can be used to perform motioncompensation.

At 1704, the process 1700 includes determining a parameter of thecurrent block. In some cases, the parameter of the current blockincludes a size of the current block. In one illustrative example, thesize of the current block can include a width of the current block. Inanother example, the size of the current block includes a height of thecurrent block. In another example, the size of the current blockincludes a width of the block and a height of the block. The size canalso include any other suitable measure of size, such as number ofpixels, area, or the like. In some cases, the parameter of the currentblock includes a chroma format of the current block. In variousexamples, the chroma format can include a 4:2:0 chroma format, a 4:2:2chroma format, a 4:4:4 chroma format, or other suitable format.

At 1706, the process 1700 includes determining at least one or more of anumber of rows of samples or a number columns of samples in a templateof the current block and at least one or more of a number of rows ofsamples or a number columns of samples in a template of a referencepicture based on the determined parameter of the current block. In oneillustrative example, when the parameter includes a width of the block,the number of rows of samples in the template of the current block isone row when the width of the current block is less than a thresholdwidth. In another illustrative example, when the parameter includes awidth of the block, the number of rows of samples in the template of thecurrent block is more than one row when the width of the current blockis greater than a threshold width. In another illustrative example, whenthe parameter includes a height of the block, the number of columns ofsamples in the template of the current block is one column when theheight of the current block is less than a threshold height. In anotherillustrative example, when the parameter includes a height of the block,the number of columns of samples in the template of the current block ismore than one columns when the height of the current block is greaterthan a threshold height. In another illustrative example, when theparameter includes a chroma format of the block, the number of rows ofsamples and the number of columns of samples in the template of thecurrent block is set to half of a luma size of the current block whenthe chroma format of the current block is 4:2:0. In another illustrativeexample, when the parameter includes a chroma format of the block, thenumber of rows of samples in the template of the current block is set toa same size as a luma size of the current block and wherein the numberof columns of samples in the template of the current block is set tohalf of the luma size when the chroma format of the current block is4:2:2.

At 1708, the process 1700 includes performing motion compensation forthe current block. Performing the motion compensation includes derivingone or more local illumination compensation parameters for the currentblock using the template of the current block and the template of thereference picture. The motion compensation can include uni-predictivemotion compensation or bi-predictive motion compensation.

When performed by a decoder, the process 1700 can further includedecoding the current block using the one or more illuminationcompensation parameters. When performed by an encoder or othertransmitter-side device, the process 1700 can include signaling the oneor more illumination compensation parameters in an encoded videobitstream.

FIG. 18 is a flowchart illustrating an example of a process 1800 ofprocessing video data using one or more of the adaptive weight selectiontechniques described herein. At 1802, the process 1800 includesobtaining a current block of a picture of the video data. In someexamples, the video data can include encoded video data (e.g., anencoded video bitstream), such as when the process 1800 is performed bya decoding device. In some examples, the video data can includeun-encoded video data, such as when the process 1800 is performed by anencoding device. The video data can include a plurality of pictures, andthe pictures can be divided into a plurality of blocks, as previouslydescribed. The video data can also include motion information for thepictures and/or blocks, which can be used to perform motioncompensation.

At 1804, the process 1800 includes obtaining a pre-defined set ofweights for template matching based motion compensation. In some cases,the predefined set of weights includes at least a first set of weightsand a second set of weights. The predefined set of weights can includemore sets of weights than the first and second sets of weights. Theweights can be used in any suitable motion compensation or estimationfunction, such as local illumination compensation, weighted prediction,or other function that uses weights for video coding.

At 1806, the process 1800 includes determining a plurality of metricsassociated with one or more spatially neighboring samples of the currentblock and one or more spatially neighboring samples of a referenceframe. For example, the plurality of metrics can be determined bydetermining a first metric by applying the first set of weights to theone or more spatially neighboring samples of the reference frame,determining a second metric by applying the second set of weights to theone or more spatially neighboring samples of the reference frame. Insome cases, the plurality of metrics can be determined by computing asum of absolute differences between the one or more spatiallyneighboring samples of the current block and the one or more spatiallyneighboring samples of the reference frame. In some cases, the pluralityof metrics can be determined by computing a sum of absolute transformeddifferences between the one or more spatially neighboring samples of thecurrent block and the one or more spatially neighboring samples of thereference frame. In some cases, the plurality of metrics can bedetermined by computing a sum of squared errors of prediction betweenthe one or more spatially neighboring samples of the current block andthe one or more spatially neighboring samples of the reference frame.

At 1808, the process 1800 includes selecting a set of weights from thepre-defined set of weights to use for the template matching based motioncompensation. The set of weights is determined based on the plurality ofmetrics. For example, the set of weights can be selected based on theplurality of metrics by comparing the first metric and the secondmetric, determining the first metric is smaller than the second metric,and selecting the first set of weights based on the first metric beingsmaller than the second metric. As indicated by the first metric beingsmaller than the second metric, the first set of weights results in asmallest metric among the pre-defined set of weights for templatematching based motion compensation.

At 1810, the process 1800 includes performing the template matchingbased motion compensation for the current block using the selected setof weights. The template matching based motion compensation can includeany suitable motion compensation technique, such as local illuminationcompensation (LIC), weighted prediction (WP), or other suitable templatematching based motion compensation technique.

In some cases, no weighting parameter is signaled with the video data.For instance, by adaptively selecting a set of weights, there is no needfor a weighting parameter to be signaled to a decoder, since the decoderis able to select the set of weights using the process

In some examples, the processes 1600, 1700, and 1800 may be performed bya computing device or an apparatus, such as the system 100 shown inFIG. 1. For example, the process 900 can be performed by the encodingdevice 104 shown in FIG. 1 and FIG. 12, by another video source-sidedevice or video transmission device, by the decoding device 112 shown inFIG. 1 and FIG. 12, and/or by another client-side device, such as aplayer device, a display, or any other client-side device. The process1000 can be performed by the encoding device 104 shown in FIG. 1 andFIG. 12, or by another video source-side device or video transmissiondevice. The process 1100 can be performed by the decoding device 112shown in FIG. 1 and FIG. 20 and/or by the encoding device 104 shown inFIG. 1 and FIG. 19. In some cases, the computing device or apparatus mayinclude a processor, microprocessor, microcomputer, or other componentof a device that is configured to carry out the steps of processes 1600,1700, and 1800. In some examples, the computing device or apparatus mayinclude a camera configured to capture video data (e.g., a videosequence) including video frames. In some examples, a camera or othercapture device that captures the video data is separate from thecomputing device, in which case the computing device receives or obtainsthe captured video data. The computing device may further include anetwork interface configured to communicate the video data. The networkinterface may be configured to communicate Internet Protocol (IP) baseddata or other type of data. In some examples, the computing device orapparatus may include a display for displaying output video content,such as samples of pictures of a video bitstream.

Processes 1600, 1700, and 1800 are illustrated as logical flow diagrams,the operation of which represent a sequence of operations that can beimplemented in hardware, computer instructions, or a combinationthereof. In the context of computer instructions, the operationsrepresent computer-executable instructions stored on one or morecomputer-readable storage media that, when executed by one or moreprocessors, perform the recited operations. Generally,computer-executable instructions include routines, programs, objects,components, data structures, and the like that perform particularfunctions or implement particular data types. The order in which theoperations are described is not intended to be construed as alimitation, and any number of the described operations can be combinedin any order and/or in parallel to implement the processes.

Additionally, the processes 1600, 1700, and 1800 may be performed underthe control of one or more computer systems configured with executableinstructions and may be implemented as code (e.g., executableinstructions, one or more computer programs, or one or moreapplications) executing collectively on one or more processors, byhardware, or combinations thereof. As noted above, the code may bestored on a computer-readable or machine-readable storage medium, forexample, in the form of a computer program comprising a plurality ofinstructions executable by one or more processors. The computer-readableor machine-readable storage medium may be non-transitory.

The coding techniques discussed herein may be implemented in an examplevideo encoding and decoding system (e.g., system 100). In some examples,a system includes a source device that provides encoded video data to bedecoded at a later time by a destination device. In particular, thesource device provides the video data to destination device via acomputer-readable medium. The source device and the destination devicemay comprise any of a wide range of devices, including desktopcomputers, notebook (i.e., laptop) computers, tablet computers, set-topboxes, telephone handsets such as so-called “smart” phones, so-called“smart” pads, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, the source device and the destination device may be equippedfor wireless communication.

The destination device may receive the encoded video data to be decodedvia the computer-readable medium. The computer-readable medium maycomprise any type of medium or device capable of moving the encodedvideo data from source device to destination device. In one example,computer-readable medium may comprise a communication medium to enablesource device to transmit encoded video data directly to destinationdevice in real-time. The encoded video data may be modulated accordingto a communication standard, such as a wireless communication protocol,and transmitted to destination device. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device to destination device.

In some examples, encoded data may be output from output interface to astorage device. Similarly, encoded data may be accessed from the storagedevice by input interface. The storage device may include any of avariety of distributed or locally accessed data storage media such as ahard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device. Destinationdevice may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In one example the source device includes a video source, a videoencoder, and a output interface. The destination device may include aninput interface, a video decoder, and a display device. The videoencoder of source device may be configured to apply the techniquesdisclosed herein. In other examples, a source device and a destinationdevice may include other components or arrangements. For example, thesource device may receive video data from an external video source, suchas an external camera. Likewise, the destination device may interfacewith an external display device, rather than including an integrateddisplay device.

The example system above is merely one example. Techniques forprocessing video data in parallel may be performed by any digital videoencoding and/or decoding device. Although generally the techniques ofthis disclosure are performed by a video encoding device, the techniquesmay also be performed by a video encoder/decoder, typically referred toas a “CODEC.” Moreover, the techniques of this disclosure may also beperformed by a video preprocessor. Source device and destination deviceare merely examples of such coding devices in which source devicegenerates coded video data for transmission to destination device. Insome examples, the source and destination devices may operate in asubstantially symmetrical manner such that each of the devices includevideo encoding and decoding components. Hence, example systems maysupport one-way or two-way video transmission between video devices,e.g., for video streaming, video playback, video broadcasting, or videotelephony.

The video source may include a video capture device, such as a videocamera, a video archive containing previously captured video, and/or avideo feed interface to receive video from a video content provider. Asa further alternative, the video source may generate computergraphics-based data as the source video, or a combination of live video,archived video, and computer-generated video. In some cases, if videosource is a video camera, source device and destination device may formso-called camera phones or video phones. As mentioned above, however,the techniques described in this disclosure may be applicable to videocoding in general, and may be applied to wireless and/or wiredapplications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by the video encoder. Theencoded video information may then be output by output interface ontothe computer-readable medium.

As noted the computer-readable medium may include transient media, suchas a wireless broadcast or wired network transmission, or storage media(that is, non-transitory storage media), such as a hard disk, flashdrive, compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from the source device and provide theencoded video data to the destination device, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from the source device and produce a disc containing the encodedvideo data. Therefore, the computer-readable medium may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

The input interface of the destination device receives information fromthe computer-readable medium. The information of the computer-readablemedium may include syntax information defined by the video encoder,which is also used by the video decoder, that includes syntax elementsthat describe characteristics and/or processing of blocks and othercoded units, e.g., group of pictures (GOP). A display device displaysthe decoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device. Various embodiments of theinvention have been described.

Specific details of the encoding device 104 and the decoding device 112are shown in FIG. 19 and FIG. 20, respectively. FIG. 19 is a blockdiagram illustrating an example encoding device 104 that may implementone or more of the techniques described in this disclosure. Encodingdevice 104 may, for example, generate the syntax structures describedherein (e.g., the syntax structures of a VPS, SPS, PPS, or other syntaxelements). Encoding device 104 may perform intra-prediction andinter-prediction coding of video blocks within video slices. Aspreviously described, intra-coding relies, at least in part, on spatialprediction to reduce or remove spatial redundancy within a given videoframe or picture. Inter-coding relies, at least in part, on temporalprediction to reduce or remove temporal redundancy within adjacent orsurrounding frames of a video sequence. Intra-mode (I mode) may refer toany of several spatial based compression modes. Inter-modes, such asuni-directional prediction (P mode) or bi-prediction (B mode), may referto any of several temporal-based compression modes.

The encoding device 104 includes a partitioning unit 35, predictionprocessing unit 41, filter unit 63, picture memory 64, summer 50,transform processing unit 52, quantization unit 54, and entropy encodingunit 56. Prediction processing unit 41 includes motion estimation unit42, motion compensation unit 44, and intra-prediction processing unit46. For video block reconstruction, encoding device 104 also includesinverse quantization unit 58, inverse transform processing unit 60, andsummer 62. Filter unit 63 is intended to represent one or more loopfilters such as a deblocking filter, an adaptive loop filter (ALF), anda sample adaptive offset (SAO) filter. Although filter unit 63 is shownin FIG. 19 as being an in loop filter, in other configurations, filterunit 63 may be implemented as a post loop filter. A post processingdevice 57 may perform additional processing on encoded video datagenerated by the encoding device 104. The techniques of this disclosuremay in some instances be implemented by the encoding device 104. Inother instances, however, one or more of the techniques of thisdisclosure may be implemented by post processing device 57.

As shown in FIG. 19, the encoding device 104 receives video data, andpartitioning unit 35 partitions the data into video blocks. Thepartitioning may also include partitioning into slices, slice segments,tiles, or other larger units, as wells as video block partitioning,e.g., according to a quadtree structure of LCUs and CUs. The ncodingdevice 104 generally illustrates the components that encode video blockswithin a video slice to be encoded. The slice may be divided intomultiple video blocks (and possibly into sets of video blocks referredto as tiles). Prediction processing unit 41 may select one of aplurality of possible coding modes, such as one of a plurality ofintra-prediction coding modes or one of a plurality of inter-predictioncoding modes, for the current video block based on error results (e.g.,coding rate and the level of distortion, or the like). Predictionprocessing unit 41 may provide the resulting intra- or inter-coded blockto summer 50 to generate residual block data and to summer 62 toreconstruct the encoded block for use as a reference picture.

Intra-prediction processing unit 46 within prediction processing unit 41may perform intra-prediction coding of the current video block relativeto one or more neighboring blocks in the same frame or slice as thecurrent block to be coded to provide spatial compression. Motionestimation unit 42 and motion compensation unit 44 within predictionprocessing unit 41 perform inter-predictive coding of the current videoblock relative to one or more predictive blocks in one or more referencepictures to provide temporal compression.

Motion estimation unit 42 may be configured to determine theinter-prediction mode for a video slice according to a predeterminedpattern for a video sequence. The predetermined pattern may designatevideo slices in the sequence as P slices, B slices, or GPB slices.Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aprediction unit (PU) of a video block within a current video frame orpicture relative to a predictive block within a reference picture.

A predictive block is a block that is found to closely match the PU ofthe video block to be coded in terms of pixel difference, which may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. In some examples, the encodingdevice 104 may calculate values for sub-integer pixel positions ofreference pictures stored in picture memory 64. For example, theencoding device 104 may interpolate values of one-quarter pixelpositions, one-eighth pixel positions, or other fractional pixelpositions of the reference picture. Therefore, motion estimation unit 42may perform a motion search relative to the full pixel positions andfractional pixel positions and output a motion vector with fractionalpixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in picture memory 64. Motion estimationunit 42 sends the calculated motion vector to entropy encoding unit 56and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Upon receiving the motion vectorfor the PU of the current video block, motion compensation unit 44 maylocate the predictive block to which the motion vector points in areference picture list. The encoding device 104 forms a residual videoblock by subtracting pixel values of the predictive block from the pixelvalues of the current video block being coded, forming pixel differencevalues. The pixel difference values form residual data for the block,and may include both luma and chroma difference components. Summer 50represents the component or components that perform this subtractionoperation. Motion compensation unit 44 may also generate syntax elementsassociated with the video blocks and the video slice for use by thedecoding device 112 in decoding the video blocks of the video slice.

Intra-prediction processing unit 46 may intra-predict a current block,as an alternative to the inter-prediction performed by motion estimationunit 42 and motion compensation unit 44, as described above. Inparticular, intra-prediction processing unit 46 may determine anintra-prediction mode to use to encode a current block. In someexamples, intra-prediction processing unit 46 may encode a current blockusing various intra-prediction modes, e.g., during separate encodingpasses, and intra-prediction unit processing 46 may select anappropriate intra-prediction mode to use from the tested modes. Forexample, intra-prediction processing unit 46 may calculaterate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and may select the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bit rate(that is, a number of bits) used to produce the encoded block.Intra-prediction processing unit 46 may calculate ratios from thedistortions and rates for the various encoded blocks to determine whichintra-prediction mode exhibits the best rate-distortion value for theblock.

In any case, after selecting an intra-prediction mode for a block,intra-prediction processing unit 46 may provide information indicativeof the selected intra-prediction mode for the block to entropy encodingunit 56. Entropy encoding unit 56 may encode the information indicatingthe selected intra-prediction mode. The encoding device 104 may includein the transmitted bitstream configuration data definitions of encodingcontexts for various blocks as well as indications of a most probableintra-prediction mode, an intra-prediction mode index table, and amodified intra-prediction mode index table to use for each of thecontexts. The bitstream configuration data may include a plurality ofintra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables).

After prediction processing unit 41 generates the predictive block forthe current video block via either inter-prediction or intra-prediction,the encoding device 104 forms a residual video block by subtracting thepredictive block from the current video block. The residual video datain the residual block may be included in one or more TUs and applied totransform processing unit 52. Transform processing unit 52 transformsthe residual video data into residual transform coefficients using atransform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform. Transform processing unit 52 may convert the residualvideo data from a pixel domain to a transform domain, such as afrequency domain.

Transform processing unit 52 may send the resulting transformcoefficients to quantization unit 54. Quantization unit 54 quantizes thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, quantization unit 54 may thenperform a scan of the matrix including the quantized transformcoefficients. Alternatively, entropy encoding unit 56 may perform thescan.

Following quantization, entropy encoding unit 56 entropy encodes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy encoding technique. Followingthe entropy encoding by entropy encoding unit 56, the encoded bitstreammay be transmitted to the decoding device 112, or archived for latertransmission or retrieval by the decoding device 112. Entropy encodingunit 56 may also entropy encode the motion vectors and the other syntaxelements for the current video slice being coded.

Inverse quantization unit 58 and inverse transform processing unit 60apply inverse quantization and inverse transformation, respectively, toreconstruct the residual block in the pixel domain for later use as areference block of a reference picture. Motion compensation unit 44 maycalculate a reference block by adding the residual block to a predictiveblock of one of the reference pictures within a reference picture list.Motion compensation unit 44 may also apply one or more interpolationfilters to the reconstructed residual block to calculate sub-integerpixel values for use in motion estimation. Summer 62 adds thereconstructed residual block to the motion compensated prediction blockproduced by motion compensation unit 44 to produce a reference block forstorage in picture memory 64. The reference block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-predict a block in a subsequent video frame or picture.

In this manner, the encoding device 104 of FIG. 19 represents an exampleof a video encoder configured to derive LIC parameters, adaptivelydetermine sizes of templates, and/or adaptively select weights. Theencoding device 104 may, for example, derive LIC parameters, adaptivelydetermine sizes of templates, and/or adaptively select weights sets asdescribed above. For instance, the encoding device 104 may perform anyof the techniques described herein, including the processes describedabove with respect to FIGS. 16, 17, and 18. In some cases, some of thetechniques of this disclosure may also be implemented by post processingdevice 57.

FIG. 20 is a block diagram illustrating an example decoding device 112.The decoding device 112 includes an entropy decoding unit 80, predictionprocessing unit 81, inverse quantization unit 86, inverse transformprocessing unit 88, summer 90, filter unit 91, and picture memory 92.Prediction processing unit 81 includes motion compensation unit 82 andintra prediction processing unit 84. The decoding device 112 may, insome examples, perform a decoding pass generally reciprocal to theencoding pass described with respect to the encoding device 104 fromFIG. 20.

During the decoding process, the decoding device 112 receives an encodedvideo bitstream that represents video blocks of an encoded video sliceand associated syntax elements sent by the encoding device 104. In someembodiments, the decoding device 112 may receive the encoded videobitstream from the encoding device 104. In some embodiments, thedecoding device 112 may receive the encoded video bitstream from anetwork entity 79, such as a server, a media-aware network element(MANE), a video editor/splicer, or other such device configured toimplement one or more of the techniques described above. Network entity79 may or may not include the encoding device 104. Some of thetechniques described in this disclosure may be implemented by networkentity 79 prior to network entity 79 transmitting the encoded videobitstream to the decoding device 112. In some video decoding systems,network entity 79 and the decoding device 112 may be parts of separatedevices, while in other instances, the functionality described withrespect to network entity 79 may be performed by the same device thatcomprises the decoding device 112.

The entropy decoding unit 80 of the decoding device 112 entropy decodesthe bitstream to generate quantized coefficients, motion vectors, andother syntax elements. Entropy decoding unit 80 forwards the motionvectors and other syntax elements to prediction processing unit 81. Thedecoding device 112 may receive the syntax elements at the video slicelevel and/or the video block level. Entropy decoding unit 80 may processand parse both fixed-length syntax elements and variable-length syntaxelements in or more parameter sets, such as a VPS, SPS, and PPS.

When the video slice is coded as an intra-coded (I) slice, intraprediction processing unit 84 of prediction processing unit 81 maygenerate prediction data for a video block of the current video slicebased on a signaled intra-prediction mode and data from previouslydecoded blocks of the current frame or picture. When the video frame iscoded as an inter-coded (i.e., B, P or GPB) slice, motion compensationunit 82 of prediction processing unit 81 produces predictive blocks fora video block of the current video slice based on the motion vectors andother syntax elements received from entropy decoding unit 80. Thepredictive blocks may be produced from one of the reference pictureswithin a reference picture list. The decoding device 112 may constructthe reference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in picture memory 92.

Motion compensation unit 82 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 82 may use one or more syntax elementsin a parameter set to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more reference picture lists for theslice, motion vectors for each inter-encoded video block of the slice,inter-prediction status for each inter-coded video block of the slice,and other information to decode the video blocks in the current videoslice.

Motion compensation unit 82 may also perform interpolation based oninterpolation filters. Motion compensation unit 82 may use interpolationfilters as used by the encoding device 104 during encoding of the videoblocks to calculate interpolated values for sub-integer pixels ofreference blocks. In this case, motion compensation unit 82 maydetermine the interpolation filters used by the encoding device 104 fromthe received syntax elements, and may use the interpolation filters toproduce predictive blocks.

Inverse quantization unit 86 inverse quantizes, or de-quantizes, thequantized transform coefficients provided in the bitstream and decodedby entropy decoding unit 80. The inverse quantization process mayinclude use of a quantization parameter calculated by the encodingdevice 104 for each video block in the video slice to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied. Inverse transform processing unit 88 applies aninverse transform (e.g., an inverse DCT or other suitable inversetransform), an inverse integer transform, or a conceptually similarinverse transform process, to the transform coefficients in order toproduce residual blocks in the pixel domain.

After motion compensation unit 82 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, the decoding device 112 forms a decoded video block by summingthe residual blocks from inverse transform processing unit 88 with thecorresponding predictive blocks generated by motion compensation unit82. Summer 90 represents the component or components that perform thissummation operation. If desired, loop filters (either in the coding loopor after the coding loop) may also be used to smooth pixel transitions,or to otherwise improve the video quality. Filter unit 91 is intended torepresent one or more loop filters such as a deblocking filter, anadaptive loop filter (ALF), and a sample adaptive offset (SAO) filter.Although filter unit 91 is shown in FIG. 17 as being an in loop filter,in other configurations, filter unit 91 may be implemented as a postloop filter. The decoded video blocks in a given frame or picture arethen stored in picture memory 92, which stores reference pictures usedfor subsequent motion compensation. Picture memory 92 also storesdecoded video for later presentation on a display device, such as videodestination device 122 shown in FIG. 1.

In this manner, the decoding device 112 of FIG. 20 represents an exampleof a video decoder configured to derive LIC parameters, adaptivelydetermine sizes of templates, and/or adaptively select weights. Thedecoding device 112 may, for example, derive LIC parameters, adaptivelydetermine sizes of templates, and/or adaptively select weights sets asdescribed above. For instance, the decoding device 112 may perform anyof the techniques described herein, including the processes describedabove with respect to FIGS. 16, 17, and 18.

In the foregoing description, aspects of the application are describedwith reference to specific embodiments thereof, but those skilled in theart will recognize that the invention is not limited thereto. Thus,while illustrative embodiments of the application have been described indetail herein, it is to be understood that the inventive concepts may beotherwise variously embodied and employed, and that the appended claimsare intended to be construed to include such variations, except aslimited by the prior art. Various features and aspects of theabove-described invention may be used individually or jointly. Further,embodiments can be utilized in any number of environments andapplications beyond those described herein without departing from thebroader spirit and scope of the specification. The specification anddrawings are, accordingly, to be regarded as illustrative rather thanrestrictive. For the purposes of illustration, methods were described ina particular order. It should be appreciated that in alternateembodiments, the methods may be performed in a different order than thatdescribed.

Where components are described as being “configured to” perform certainoperations, such configuration can be accomplished, for example, bydesigning electronic circuits or other hardware to perform theoperation, by programming programmable electronic circuits (e.g.,microprocessors, or other suitable electronic circuits) to perform theoperation, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software,firmware, or combinations thereof. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present invention.

The techniques described herein may also be implemented in electronichardware, computer software, firmware, or any combination thereof. Suchtechniques may be implemented in any of a variety of devices such asgeneral purposes computers, wireless communication device handsets, orintegrated circuit devices having multiple uses including application inwireless communication device handsets and other devices. Any featuresdescribed as modules or components may be implemented together in anintegrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a computer-readable data storage mediumcomprising program code including instructions that, when executed,performs one or more of the methods described above. Thecomputer-readable data storage medium may form part of a computerprogram product, which may include packaging materials. Thecomputer-readable medium may comprise memory or data storage media, suchas random access memory (RAM) such as synchronous dynamic random accessmemory (SDRAM), read-only memory (ROM), non-volatile random accessmemory (NVRAM), electrically erasable programmable read-only memory(EEPROM), FLASH memory, magnetic or optical data storage media, and thelike. The techniques additionally, or alternatively, may be realized atleast in part by a computer-readable communication medium that carriesor communicates program code in the form of instructions or datastructures and that can be accessed, read, and/or executed by acomputer, such as propagated signals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC).

What is claimed is:
 1. A method of processing video data, the method comprising: obtaining a current block of a picture of the video data; determining a parameter of the current block; determining at least one or more of a number of rows of samples or a number columns of samples in a template of the current block and at least one or more of a number of rows of samples or a number columns of samples in a template of a reference picture based on the determined parameter of the current block; and performing motion compensation for the current block, wherein performing the motion compensation includes deriving one or more local illumination compensation parameters for the current block using the template of the current block and the template of the reference picture.
 2. The method of claim 1, wherein the parameter of the current block includes a size of the current block.
 3. The method of claim 2, wherein the size of the current block includes a width of the current block.
 4. The method of claim 3, wherein the number of rows of samples in the template of the current block is one row when the width of the current block is less than a threshold width.
 5. The method of claim 3, wherein the number of rows of samples in the template of the current block is more than one row when the width of the current block is greater than a threshold width.
 6. The method of claim 2, wherein the size of the current block includes a height of the current block.
 7. The method of claim 6, wherein the number of columns of samples in the template of the current block is one column when the height of the current block is less than a threshold height.
 8. The method of claim 6, wherein the number of columns of samples in the template of the current block is more than one columns when the height of the current block is greater than a threshold height.
 9. The method of claim 2, wherein the size of the current block includes a width of the block and a height of the block.
 10. The method of claim 1, wherein the parameter of the current block includes a chroma format of the current block.
 11. The method of claim 10, wherein the number of rows of samples and the number of columns of samples in the template of the current block is set to half of a luma size of the current block when the chroma format of the current block is 4:2:0.
 12. The method of claim 10, wherein the number of rows of samples in the template of the current block is set to a same size as a luma size of the current block and wherein the number of columns of samples in the template of the current block is set to half of the luma size when the chroma format of the current block is 4:2:2.
 13. The method of claim 1, further comprising decoding the current block using the one or more illumination compensation parameters.
 14. The method of claim 1, further comprising signaling the one or more illumination compensation parameters in an encoded video bitstream.
 15. An apparatus comprising: a memory configured to store video data; and a processor configured to: obtain a current block of a picture of the video data; determine a parameter of the current block; determine at least one or more of a number of rows of samples or a number columns of samples in a template of the current block and at least one or more of a number of rows of samples or a number columns of samples in a template of a reference picture based on the determined parameter of the current block; and perform motion compensation for the current block, wherein performing the motion compensation includes deriving one or more local illumination compensation parameters for the current block using the template of the current block and the template of the reference picture.
 16. The apparatus of claim 15, wherein the parameter of the current block includes a size of the current block.
 17. The apparatus of claim 16, wherein the size of the current block includes a width of the current block.
 18. The apparatus of claim 17, wherein the number of rows of samples in the template of the current block is one row when the width of the current block is less than a threshold width.
 19. The apparatus of claim 17, wherein the number of rows of samples in the template of the current block is more than one row when the width of the current block is greater than a threshold width.
 20. The apparatus of claim 16, wherein the size of the current block includes a height of the current block.
 21. The apparatus of claim 20, wherein the number of columns of samples in the template of the current block is one column when the height of the current block is less than a threshold height.
 22. The apparatus of claim 20, wherein the number of columns of samples in the template of the current block is more than one columns when the height of the current block is greater than a threshold height.
 23. The apparatus of claim 16, wherein the size of the current block includes a width of the block and a height of the block.
 24. The apparatus of claim 15, wherein the parameter of the current block includes a chroma format of the current block.
 25. The apparatus of claim 24, wherein the number of rows of samples and the number of columns of samples in the template of the current block is set to half of a luma size of the current block when the chroma format of the current block is 4:2:0.
 26. The apparatus of claim 24, wherein the number of rows of samples in the template of the current block is set to a same size as a luma size of the current block and wherein the number of columns of samples in the template of the current block is set to half of the luma size when the chroma format of the current block is 4:2:2.
 27. The apparatus of claim 15, further comprising: a display for displaying the video data.
 28. The apparatus of claim 15, wherein the apparatus comprises a mobile device with a camera for capturing pictures.
 29. A non-transitory computer-readable medium having stored thereon instructions that, when executed by one or more processors, cause the one or more processor to: obtain a current block of a picture of video data; determine a parameter of the current block; determine at least one or more of a number of rows of samples or a number columns of samples in a template of the current block and at least one or more of a number of rows of samples or a number columns of samples in a template of a reference picture based on the determined parameter of the current block; and perform motion compensation for the current block, wherein performing the motion compensation includes deriving one or more local illumination compensation parameters for the current block using the template of the current block and the template of the reference picture.
 30. An apparatus for processing video data, comprising: means for obtaining a current block of a picture of the video data; means for determining a parameter of the current block; means for determining at least one or more of a number of rows of samples or a number columns of samples in a template of the current block and at least one or more of a number of rows of samples or a number columns of samples in a template of a reference picture based on the determined parameter of the current block; and means for performing motion compensation for the current block, wherein performing the motion compensation includes deriving one or more local illumination compensation parameters for the current block using the template of the current block and the template of the reference picture. 